If they are registered after 23rd January I think it's the higher rate, mine was registered 26th January!!! Doh!!
However I have been thinking about contacting the DVLA, here's the reason.......
I had a Datsun 240Z that was registered January 1st 1975, all 240Z's were 'built' in1969, apparently they didn't think they would sell so many so did them in one go, painted and ready to go, I got a letter of authentication from the classic Z register and as a result didn't have to pay road tax, eg pre 1973 build, my ///M says built January 2006, wondering if I can find out actual build date and see if the DVLA would accept and as a result get the lower RFL, you never know?