BSG is a combined UK/Canada/USA production. I think they missed a nice opportunity by not declaring that various colonies had various Canadian, American, British and other English-speaking nation's accents. Then most of the actors could work in their natural accent, though a few would have to switch, which of course they are capable of.
Not too many though. It's perfectly possible for a military father like Adama to have a different accent from his son Lee (who in real life has a strong British/Irish accent) by explaining that as a military brat, he grew up on a a different world, his father mostly absent in space. Many characters come from Caprica (which would presumably be assigned one of the Canadian or American accents) but because Caprica was the colonial capital, it would be pretty easy to explain characters there as immigrants. Aside from allowing actors to focus on other things besides doing the right accent, this would also have added a nice touch of character to the show, since we don't normally get a sense of these people as being from different planets which only united in CW1 the way we should.