RP = Received Pronunciation. It's the way that traditionally a BBC newsreader will speak. RP actually originated in the South East a couple of hundred years ago, and was propegated by the public school system. There's a lot of variation in RP - from the modified 50s style of the Queen to the modern upper class sort of blase drawl, but 'BBC English' can be seen as its yard stick. Most RP speakers are under the impression that they don't have an accent at all, which is quite funny. Modified RP is where there are some regional elements - for example, the northern shorter 'a' in words like 'bath', rather than the southern 'ar'. It doesn't sound as 'posh' as RP, but it's not a definite regional accent.

Ticking of subsets isn't a problem btw - I'll just take the most specific answer as being the accent people think I have. I just had some problems with people ticking accents that were totally different to each other. One respondant ticked Brummy *and* Scouse, for example, so I'm not sure what to do with results like that.