If you have any accounts with Nationwide, talk to them:
They offer 'FREE' annual cover for most account holders, but there is a premium for pre-existing conditions, so you ring em up, answer about ten questions (none difficult), and end up paying about £140 for a year, covering pretty much the whole world.
I agree with Stuc that PC is most unlikely to suddenly cause an unforeseen overseas catastrophe, and (while we're in the EU!), the EHIC card gives you full access to health care. You wouldn't get insurance to from London to Edinburgh or Belfast - really no difference these days!
Going outside the EU is a different ball game, and PC isn't the only issue, you might fall over and bang your knee if the beer's good ;-)
Peggy: Talk to your insurer: you may end up paying a little more. But if they don't know, your policy is invalid. Keeping them informed is a condition on all health insurance :-) And if they ask too much - read the whole thread and get a new policy with a better insurer!