Dont know of a good one in surry but my retrim was done on the south cost by Mark Thomas Triming tel no 01903851559. There is a trimmers just by Abbey who have a vehicle section try asking Mark what they are like.
I was hoping that you would chip in John. It's not for leather or anything posh. I fancy cutting the seats to fit around the cage so that they don't look pinched where the cage and seat are fighting for space.