I want to enrol on a phd.

I have a degree in business from some 10 years ago.

Can anyone suggest a way in since I only got a 2:2 and want to do further study.

I am interested in a social science topic.

Probably the best way to begin is by enrolling in some grad courses at a local university on a continuing education basis. This will allow you to check out various programs, and earn the course credits necessary to counter your 2.2 GPA. Just be sure that you earn As in the courses you take. You can also use the professors from those continuing education courses to write you letters of recommendation for admittance.

Business to social science is a bit of a leap. You'd probably have to take a taught Masters degree first, in the topic you're interested in, (1) to overcome your 2.2 which would be somewhat difficult to be admitted to a PhD with; and (2) to start to build up the specialist knowledge in your new field. Normally you'd need to fund that Masters yourself, even if you were (possibly unlikely, with that 2.2) to win funding for the PhD afterwards.