Thought I would follow-up on this one, after all the haggling and ringing around, I found that Churchill doesn't punish you for the change, I have credit for my US license years of experience and full credit for no claims. So it was a small increase in the premium, but had a few extra benefits that were better than what I had, so all in all it's sorted after some pain.
Thanks for the tips too, that was helpful, I was about to go the direction you suggested with a broker, but found these guys. So now once I get a year or two under my belt with the UK license I hope I'll be back to normal.