Not a question that I can answer with certainty, sorry Dermot.
There have not actually being that many females who have acceded to the throne of England or (after the Union) Britain. I suppose the first one (for more than a few weeks, anyway

) was Henry 8's daughter Mary.
As she was married to Philip, King of Spain, he was a King in his own right. However he also did not speak a word of English & was not exactly a popular figure amongst the aristocracy either. Hence Parliament actually wrote into the constitution that Philip would only be considered the ruler of England for as long as Mary was alive.
Mary died, Elizabeth 1st. took over as Queen. Philip & Elizabeth (& so Spain & England) became quite the worst of enemies. As Elizabeth did not marry, she did not have a partner to call anything.
The next female to reign was Mary 2nd. with her husband William. This is a bit of a difference in that her husband was actually called King William 3rd. - also known as William of Orange. However this was not an inherited assent to the throne. The PAIR were offered the 'job' by Parliament who had overthrown James 2nd. The couple were offered the position because they were both grandchildren of Charles 1st. & both staunchly Protestant, rather than Catholic like James.
They (or rather William who ruled for 8 years on his own when his wife died) were succeeded by another female Queen Ann, Mary's sister.
However William, Mary & Ann all ascended to the crown under Acts of Parliaments - for the first time ever.
Specifically the Bill of Rights 1689 & Act of Settlement 1701. These 2 Acts of Parliament contain most of the law concerning who can, and can't, rule Britain.
I would think that the convention that the husband of the Queen is not entitled King is probably contained somewhere within these acts. However, I am not sure if it is actually written anywhere or if it is just something that has never previously happened & so is unlikely to in the future, or is as Seahawk's logical reply.