Thank you Nigel for that very informative reply. The timing of the 1869 Act actually answers most of my questions.

However, I'm still wondering about this situation: in a Will dated 1902 the eldest son is only mentioned when being excluded from benefitting from one particular legacy and the mother/executrix, who is left the 'whole of my real and personal estate' 'to be disposed of by her as in her judgment may seem right', seems to have died without leaving a Will about 20 years later. I'm wondering if it's possible to work out where this leaves the eldest son!

Thanks again for your initial reply.