I use Imaging Insurance, was recommended to me by a couple of pros 2 years ago when I was looking, though I've not had to claim so I can't comment on that side.
http://www.imaginginsurance.co.uk/
One of the people who recommended them had 3 claims in 3 years & said they were very good, quick & professional, but of course, that's second hand info, or is it third hand now I've told you?