I think Ms O'Ftroy (a contraction of the Irish Fitzroy perhaps) is correct with her supposition. The letters were there to help with named exchanges, were dropped when they limited the expansion, and have been revived to cater for text entry for various applications.

UK has had two major changes in recent years; London and a few other places changed twice. Some of the changes helped ("08" means a reduced charge of some kind, "09" a premium rate) and new numbers are of the format 012-3456-7890. And for some obscure reason the first digit on all numbers is always "0" which is dropped when calling from abroad.

Rod