Hello Mick,

If these are births registered in England or Wales, the most likely reason they are indexed under two surnames is because, as you say, the parents weren't married.

If you have index entries which look something like this:

1950 Jan-Feb-Mar, SMITH Robert, [mother's maiden name] JONES, Anytown, [vol] 1, [page] 20
1950 Jan-Feb-Mar, JONES Robert, [mother's maiden name] JONES, Anytown, [vol] 1, [page] 20

... then the birth certificate will contain something like this:

Father's name: John SMITH
Mother's name: Sarah JONES

Or if the mother had previously been married, but not to the father, the index entries might look something like this:

1950 Jan-Feb-Mar, SMITH Robert, [mother's maiden name] WILSON, Anytown, [vol] 1, [page] 20
1950 Jan-Feb-Mar, JONES Robert, [mother's maiden name] WILSON, Anytown, [vol] 1, [page] 20

... and the birth certificate will contain something like this:

Father's name: John SMITH
Mother's name: Sarah JONES formerly WILSON

There are other reasons why births could be registered in more than one name, such as the mother might have been known by more than one surname, but the above is the most likely cause. Of course, you'll probably know if this is the case depending on whether the names match up or not. :-)

Christine