Have a check on the CTC forum, there seems to be dissention in the ranks on the future direction they are taking and issues round making Chris Juden redundant seeing people getting jumpy.
*edit, Crossed with Reg above*
I looked at both and largely much of a muchness, BC maybe a bit cheaper and more race oriented but chiming in with commuting and the mass participation rides. Decided on neither at the end of it though, I show my support for cycling by being out there doing it and getting involved at a local level with my Council cycling forum. Incidentally which neither local elements of CTC or BC attend.