if you want British regions then you have to decide what level you want to go to.
traditionally the counties were the sub dividisions in the UK. These had been the fixed adminstrative areas for hundreds of years. possibly dating back to before the time of the Normans. in 1974 these administrative areas were modified, with new areas created out of existing counties
ferinstance Lancashire lost part of its territory to the new counties of Greater Manchester, Merseyside & Cumbria.
since then the politicians have been meddling again, hiving off different bits of the historic countres into new administrative areas.
ferinstance Cheshire has now been split into two entites East & West Cheshire.
Im guessing for your purposes the 1974 reorgansiation is probably the most relevant to what you want. as this is the more commonly used notation these days. however unlike the US these boundaries are not set in stone and different counties have different 'acceptance' in the population. some counties are still very clear in their indentity (eg Yorkshire (even though as a county Yorkshire ceasaed to exist in 1974 when its constituent parts (the ridings there broken up and reallocated), Cornwall and so on. not many identify themsleves as 'belonging to the 1974 metropolitan counties of Greater London, Greater Manchester, Merseyside, West Midlands and so on
you could probably codge together a list based on
List of counties of the United Kingdom - Wikipedia, the free encyclopedia
however since 200 the Post Office / Royal Mail have announced that they no longer see the need for the county to be put in an address as their internal postcode system is sufficient to identify an address and therefore no longer need the county to localise a specific 'main street'.
http://en.wikipedia.org/wiki/Postal_..._United_Kingdo
the (UK) post code as 4 elements
the first being the nearest main sorting office,
the next being an area the delivery office
the next being the delivery round
the last being a specific geographical area that should target upto 10..20 addresses.