Ryan Rotary in Wantage are possibly the closest or HME in Coventry.
My recommendation is Rotary Motion near Chippenham, I have had a few done there , currently in my possession is a four port RX-8 which was rebuilt by them around 15k miles ago and has very good compression.
I've just had my 231 engine rebuilt by Ryan rotary and they've done a splendid job, I went for a street port with auxilary bridge and there's a lot more power than before and so smooth plus it comes with a 12K / 1 year warrenty