Just to add, many policies state that they only cover permanent residents, but if you enquire further they will almost always say that for their purposes, a permanent resident is someone who lives in the UK more than 6 months in the year and is registered with a UK GP. I have not once found a travel insurer that said they considered a permanent resident to be someone with ILR. So basically any travel insurer should be OK as long as you get them to put their definition of permanent resident in writing (if it is not already specified in the policy documentation, which it sometimes is).
I personally took out a Nationwide FlexAccount, which provides a free European travel insurance policy that can be upgraded to worldwide for £20 a year.