I'm guessing from the number that this is the ESRC (economic and social research council) DTCs - if so the list is here (note it's more than 21 universities as most are in consortia):
http://www.esrc.ac.uk/funding-and-guidance/guidance/postgraduates/doctoral-training-centres.aspx
Other research councils I think are also looking at concentrating funded PhDs in a smaller group of DTCs like the EPSRC do already.
Other universities can still offer PhDs in those academic areas but the training they offer was not considered strong enough to merit these research councils funding students there.
The ESRC decision has been very controversial, as it's cut out pretty much all post 92 universities along with some pre 92 ones from funding, and people say that it will be very hard for such universities to gain recognition in the future because they will have had 5 years with no institutional requirement to fund good social science research methods training, and in these straitened times, that means they probably would cut it.