Thanks ShaunJ,
I should have mentioned that I did a lot of (mostly internet-based) research and found no evidence to support the story of my great grandfather's Regent Street birth.
The story is that he (Edmund Browne) was born (c1860) in Regent Street "on the site where the Galeries Lafayette later stood", but that his family returned to Ireland soon after he was born.
We've now found birth/baptism records for siblings from 1867 onwards in Co Tipperary and are assuming that his birth wasn't registered in England, and that he was baptised in Ireland.
The story may still be true, but I don't think we'll find any documentary evidence.
Pete
P.S. I was in the UK in Jun/Jul this year, and checked the original London Directories for 1861-1864 at the TNA. The block covering 172-206 Regent Street was between Chapel Court and Foubert's Place. Hamleys is now at 188-196, in the block between Foubert's Place and Tenison Court. The numbering seems to have stayed the same. (Foolishly I didn't look at the 1920s-1960s directories to confirm the exact location of the Galeries Lafayette!).
This contradicts Gadget's recollection that it was "...on the curve of Regent Street - on the East side towards the bottom end...". Is it possible that they had two shops on Regent Street?