A lot of company's could remove and refit the engines but the UK is a bit short of good places to get the engine (s) stripped and released for further service.
I will recomend Nicholson Mclaren, they have done some engine work for me and have always produced a first class product at a reasonable cost.
Also a company that I have not had any dealings with but comes with a good reputation is (I think the spelling is correct) Van eisenburg engineering at Southend.
I doubt that these company's will be the cheapest quotes but the quality of work will save you a lot in the long run.