In England the list of forbidden marriages was drawn up by the Church of England in 1560 and remained unchanged until the 20th century. I have reproduced the original list below. Because it is presented in a precise but rather complicated way I have transformed the list into a more easily understood form here .

Table 22 List of Forbidden Marriages



A Man may not marry his

A Woman may not marry her

1 Grandmother

1 Grandfather

2 Grandfather's Wife

2 Grandmother's Husband

3 Wife's Grandmother

3 Husband's Grandfather

4 Father's Sister

4 Father's Brother

5 Mother's Sister

5 Mother's Brother

6 Father's Brother's Wife

6 Father's Sister's Husband

7 Mother's Brother's Wife

7 Mother's Sister's Husband

8 Wife's Father's Sister

8 Husband's Father's Brother

9 Wife's Mother's Sister

9 Husband's Mother's Brother

10 Mother

10 Father

11 Stepmother

11 Stepfather

12 Wife's Mother

12 Husband's Father

13 Daughter

13 Son

14 Wife's Daughter

14 Husband's Son

15 Son's Wife

15 Daughter's Husband

16 Sister

16 Brother

17 Wife's Sister

17 Husband's Brother

18 Brother's Wife

18 Sister's Husband

19 Son's Daughter

19 Son's Son

20 Daughter's Daughter

20 Daughter's Son

21 Son's Son's Wife

21 Son's Daughter's Husband

22 Daughter's Son's Wife

22 Daughter's Daughter's Husband

23 Wife's Son's Daughter

23 Husband's Son's Son

24 Wife's Daughter's Daughter

24 Husband's Daughter's Son

25 Brother's Daughter

25 Brother's Son

26 Sister's Daughter

26 Sister's Son

27 Brother's Son's Wife

27 Brother's Daughter's Husband

28 Sister's Son's Wife

28 Sister's Daughter's Husband

29 Wife's Brother's Daughter

29 Husband's Brother's Son

30 Wife's Sister's Daughter

30 Husband's Sister's Son

Table 23 Simplified List of Forbidden Marriages - A Table of Kindred and Affinity, (1560 list)

Wherein whosoever are related are forbidden in scripture and our laws to marry together

A Man may not marry his

A Woman may not marry her

1 Grandmother

1 Grandfather

2 Stepgrandmother

2 Stepgrandfather

3 Grandmother-in-Law

3 Grandfather-in-Law

4-5 Aunt

4-5 Uncle

6-9 Aunt-in-Law

6-9 Uncle-in-Law

10 Mother

10 Father

11 Stepmother

11 Stepfather

12 Mother-in-Law

12 Father-in-Law

13 Daughter

13 Son

14 Stepdaughter

14 Stepson

15 Daughter-in-Law

15 Son-in-Law

16 Sister

16 Brother

17-18 Sister-in-Law

17-18 Brother-in-Law

19-20 Granddaughter

19-20 Grandson

21-22 Granddaughter-in-Law

21-22 Grandson-in-Law

23-24 Stepgranddaughter

23-24 Stepgrandson

25-26 Niece

25-26 Nephew

27-30 Niece-in-Law

27-30 Nephew-in-Law

No cousins are mentioned, which is surprising since double first cousins (first degree and normal) are equivalent in their relationships to full and half sibs respectively. Also, half sibs are not mentioned, but I think the inclusion of half sibs is implicit in the general terms 'brother' or 'sister'.In the same vein half uncles, half aunts, half nephews and half nieces are implicitly included with their full counterparts.This is made clearer in later lists where half sibs are referred to specifically.

The full set of in-laws and step relatives are included to match the equivalent blood relatives of the same name except the following:

It seems strange excluding stepbrothers and stepsisters while including stepsons and stepdaughters. The first changes were made in 1907:

The 1907 Marriage Act removed no. 17 from the forbidden list (Wife's sister and Husband's brother), provided the first spouse in each case was deceased. Further changes followed in 1921, 1931 and 1949:

The 1921 Marriage Act removed no. 18 (Brother's wife and Sister's husband) provided brother or sister in each case was deceased.

The 1931 Marriage Act removed 6, 7, 8 and 9 (Aunt-in-law and Uncle-in-law) and 27, 28, 29 and 30 (Niece-in-law and Nephew-in-law), provided the relevant Uncle, Aunt, Niece, and Nephew were dead.

The 1949 Marriage Act confirmed the previous 3 acts and specifically included 'half blood' relatives.

Table 24 List of Forbidden Marriages (1949 version)



A man may not marry his:

A woman may not marry her:

1 Mother

1 Father

2 Daughter

2 Son

3 Father' Mother

3 Father's Father

4 Mother's Mother

4 Mother's Father

5 Son's Daughter

5 Son's Son

6 Daughter's daughter

6 Daughter's son

7 Sister

7 Brother

8 Father's Daughter

8 Father's Son

9 Mother' Daughter

9 Mother's Son

10 Wife's Mother

10 Husband's father

11 Wife's Daughter

11 Husband's Son

12 Father's Wife

12 Mother's Husband

13 Son's Wife

13 Daughter's Husband

14 Father's Father's Wife

14 Father's Mother's Husband

15 Mother's Father's Wife

15 Mother's Mother's Husband

16 Wife's Father's Mother

16 Husband's Father's Father

17 Wife's Mother's Mother

17 Husband's Mother's father

18 Wife's Son's Daughter

18 Husband's Son's Son

19 Wife's Daughter's Daughter

19 Husband's Daughter's Son

20 Son's Son's Wife

20 Son's Daughter's Husband

21 Daughter's Son's Wife

20 Daughter's Daughter's Husband

22 Father's Sister

22 Father's Brother

23 Mother's Sister

23 Mother's Brother

24 Brother's Daughter

24 Brother's Son

25 Sister's Daughter

25 Sister's Son

Table 25 Simplified List of Forbidden Marriages (1949 version)

A man may not marry his:

A woman may not marry her:

1 Mother

1 Father

2 Daughter

2 Son

3-4 Grandmother

3-4 Grandfather

5-6 Granddaughter

5-6 Grandson

7 Sister

7 Brother

8-9 Half Sister

8-9 Half Brother

10 Mother-in-Law

10 Father-in-Law

11 Stepdaughter

11 Stepson

12 Stepmother

12 Stepfather

13 Daughter-in-Law

13 Son-in-Law

14-15 Stepgrandmother

14-15 Stepgrandfather

16-17 Grandmother-in-Law

16-17 Grandfather-in Law

18-19 Stepgranddaughter

18-19 Stepgrandson

20-21 Granddaughter-in-Law

20-21 Grandson-in-Law

22-23 Aunt and Half Aunt

22-23 Uncle and Half Uncle

24-25 Niece and Half Niece

24-25 Nephew and Half Nephew

To emphasise that the ten 'in-law' relatives, removed from the above list, could only marry the nominated person if all previous spouses were dead, a second list was included:

Table 26 In-laws Whom the Nominated Person Can Marry With the Above Restrictions (1949 Act)

1. Deceased wife's sister

1. Deceased sister's husband

2. Deceased brother's wife

2. Deceased husband's brother

3. Deceased wife's brother's daughter

3. Deceased husband's brother's son

4. Deceased wife's sister's daughter

4. Deceased husband's sister's son

5. Brother's deceased son's wife

5. Brother's deceased daughter's husband

6. Sister's deceased son's wife

6. Sister's deceased daughter's husband

7. Father's deceased brother's wife

7. Father's deceased sister's husband

8. Mother's deceased brother's wife

8. Mother's deceased sister's husband

9. Deceased wife's father's sister

9. Deceased husband's father's brother

10. Deceased wife's mother's sister

10. Deceased husband's mother's brother

Table 27 Simplified Version of Table 26

1-2 Sister-in-law

1-2 Brother-in-law

3-6 Niece-in-law

3-6 Nephew-in-law

7-10 Aunt-in-law

7-10 Uncle-in-law

Current Regulations (1986)

Since 1949 there have been several further Marriage Acts culminating in the 1986 Act which brought the regulations up to date.

Blood Relatives

The following blood relatives are still forbidden to marry under all circumstances:

Table 28 Blood Relatives Forbidden to Marry

A man may not marry his:

A woman may not marry her:











Half Sister

Half Brother



Half Aunt

Half Uncle



Half Niece

Half Nephew

In 1960 the restrictions on the in-law relatives mentioned in tables 26 and 27 were removed. This means they are now free to marry irrespective of whether the former spouse is dead. i.e. It allows divorcees in this category to remarry.

The following in-laws can also marry without any restrictions, i.e. regardless of whether or not their first spouses are still alive:

Table 29 Further In-laws Who Can Marry Without Restrictions

A man can marry his:

A woman can marry her:

Former wife's father's mother

Former husband's father's father

Former wife's mother's mother

Former husband's mother's father

Son's son's former wife

Son's daughter's former husband

Daughter's son's former wife

Daughter's daughter's former husband

The remaining step relatives can now marry provided they are over 21. Also, the younger person must not have been treated as a child of the older person's family and never, under the age of 18, lived under the same roof as the older person.

Table 30 Step relatives Who Can Marry With the Above Restrictions

A man can marry his:

A woman can marry her:

Former wife's daughter

Former husband's son

Father's former wife

Mother's former husband

Father's father's former wife

Father's mother's former husband

Mother's father's former wife

Mother's mother's former husband

Former wife's son's daughter

Former husband's son's son

Former wife's daughter's daughter

Former husband's daughter's son

The remaining in-laws can now also marry provided they are both over 21 and any former spouses must be deceased.

Table 31 In-laws Who Can Marry With the Above Restrictions

A man can marry his:

A woman can marry her:

Former wife's mother

Former husband's father

Son's former wife

Daughter's former husband

A new forbidden category has now been added covering adopted children:

Table 32 Relatives by Adoption Who Are Forbidden to Marry

A man may not marry his:

A woman may not marry her:

Adoptive mother or former adoptive mother

Adoptive father or former adoptive father

Adopted daughter or former adopted daughter

Adopted son or former adopted son

Surprisingly marriage between unrelated adopted brothers and sisters (i.e. adopted by the same adoptive parents) is allowed.

The marriage laws for Scotland and Northern Ireland are similar to England and Wales except that Scotland also includes the following forbidden blood relationships:

Table 33 Further Forbidden Marriages (Scotland

A man may not marry his:

A woman may not marry her:





Comments on the 1986 Regulations

My criticism is that there are still no sensible rules about marriage between 'blood' relatives. The only logical way would be to fix an obligate level of inbreeding beyond which it is not permissible to go. For example, if the maximum coefficient of relationship between partners is fixed at 1/8, this would limit the coefficient of inbreeding to 1/16 (6.25%). Marriages between single first cousins would then still be allowed but not between double first cousins. It would also allow unions between half uncle and half niece and between half aunt and half nephew. If this was introduced the list of forbidden marriages between'blood' relatives would then become:








Full Sib



Half Sib



Double First Cousins (first degree)



Double First Cousins






Uncle-niece and Aunt-nephew


Also any other unusual cousin or other relationships with an R value of 1/4 or above (see enhanced relationships.)

These figures could only be used as a guide since previous inbreeding (known or unknown), particularly in small closed populations could cause nominally low relationships such as first cousin (R = 1/8) to rise above 1/4. In these special situations it would be necessary to have a genetically qualified panel to assess the wisdom of certain marriages. The presence of any known inherited abnormalities in a family would also have to be taken into account.


Incest is defined by Martin (1990) as: ''Sexual intercourse between a man and his mother, daughter, sister, half sister or granddaughter, or between a woman over the age of 16 and her father, son, brother, half brother or grandfather. Even if both partners consent, incest is a criminal offence if the partners know of their relationship. It is punishable by up to 7 years imprisonment (or, with a girl under 13, by a maximum sentence of life imprisonment), but no prosecution can be brought without the consent of the Director of Public Prosecutions. The relationships listed above include illegitimate relationships. It is a statutory offence for a man to incite a girl to have incestuous intercourse with him, but being under 16, she would not be guilty of any crime if intercourse took place.''


Apart from religious constraints, the idea that incest laws should only encompass members of the close family stems from the desire to protect vulnerable children. From the biological point of view, however, all close inbreeding is harmful and undesirable, even when it involves relatives outside the nuclear family.

The above list excludes several relationships which are as close or even closer, in terms of the coefficient of relationship, than those within it. The following are some examples:

  • Grandmother-grandson. This is a sexist exclusion, since although Grandfather-granddaughter incest is more likely to happen, when Grandmother-grandson incest does occur it is just as serious.
  • Uncle-niece and Aunt-nephew sexual unions are excluded even though their coefficients of relationship are the same as between Half sibs and Grandfather-granddaughter (R = 1/4).
  • Double first cousins of both types (first degree and normal), with R values equal to Full and Half sibs respectively, are also excluded. Likewise any of the other unusual cousin relationships described earlier, with coefficients of relationship of 1/4 or above. In view of the severity of the punishment for statutory incest I think these close cousin relationships should at least be included among the list of forbidden marriages.

[18] 1955 edition of the Book of Common Prayer (Church of England)

[17] Taken from the 1908 edition of The Book of Common Prayer (Church of England)