I would imagine most of them do - but you have to be honest with them, if you fail to declare a pre-existing condition, you risk invalidating your cover. Ring round, and have a preliminary chat with a few.
Not sure I would agree with you Andy - most medical insurance policies specifically deny pre-existing medical conditions. I know this as a diabetic. However, as Andy says, talk to the brokers, they may be able to arrange somethiing, but it would be expensive, unless you can prove that the condition is not likely to cause problems.
I stand corrected HitMaker - I was basing my answer on personal experience - my wife has asthma, which we declared for travel insurance with no problems, but on reflection, a company may wish to avoid potential complications involved in more serious conditions. As we agree, it is best to run the specifics past individual companies for a more specific response.