Was just amused, reading a book set in WW2 (the latest Maisie Dobbs if there are other fans out there!) in which Maisie explains that 'taxi' is used by Americans, and British people say 'cabs'.
The author (Jacqueline Winspear) is usually spot on with her research - indeed her own older relatives are one of her sources, so I'm sure it is accurate.
I do say 'cab' occasionally - usually in London when I think about it - but I'm sure that 'taxi' was in common use in my 50s childhood. Was there a difference between London and the rest of GB?