There are as many, if not more regional accents in the UK than there are in the US. The history of the English language is quite interesting once you start to dig. Some of the British seem to make out a distinct separation from their European origins (in this writers experience) where they are as diverse historically as the Americas.

Speech Accent Archive - Audio examples of different English accents worldwide. (For England, click on “english” in the left column. Requires Quicktime plugin.)

Eviews Interviews on the Net A library of interviews classified by region.

University College London, Professor Wells Course guide to English accents - An in depth course about English accents, if you want to dig deeper. (pdf files)

Will you lose your American accent?

It depends. Most likely not unless you try to. However, after 5+ years, you might expect to have a some mutation of an accent that will confuse people! If you have children that are being raised in the UK, you would do well to talk to them in the native terminology to prevent extra teasing at school.

Bob comments: "The Brits are very aware of their history and know they are an amalgam of Celtic, Norwegian and Danish Vikings, Northern Germans (Angles and Saxons), Norman French and a host of other peoples who have settled in the British Isles over many centuries.  Indeed, all these different peoples migration goes a long way to explain the plethora of local accents and dialects and at least two Celtic  languages: Welsh and Scots Gaelic) found in such a small island."