For better or worse, the UK now has a marketised HE sector. That means that of course there will be a university somewhere which will accept you for postgraduate study; you may just have to compromise on prestige and bankability.
I'm not sure either that I accept wholly the arguments put forward more or less delicately by some posters above that anything less than a 2:1 signifies extreme dimness, that there is some sort of cliff edge of cleverness. People underachieve in their first degree for any number of reasons. I'm doing a PhD at a world-class university with someone who got a third in her UG degree, which was in a subject she later thought she had chosen mistakenly. She went off to work and volunteer for a while, then came back and did a Master's in a field much more suited to her, gaining a Credit. This got her onto the PhD. We have all had to do compulsory research methods modules, and she has got an average of Distinction. The woman is getting better and better, but would have been written off by many of the people posting here. I agree that grades are useful and necessary, but that doesn't mean that human ability and capacity are fixed and unable to be developed.