PhD's tend to be advertised on University websites, jobs.ac.uk and findaphd.com Best to keep on an eye on these websites to see if anything appeals.
If you get funding, which I think is on average just over £13,000 (not taxed on it) it normally does not extend beyond 3 years and so you may need to factor this in when making a decision as to whether or not to do one.
It can be difficult getting secure employment after finishing a PhD and so this may be something else for you to take into consideration.
Good luck with whatever you decide.