there is one in harlow (just outside north london) that me and my guys have used many times and is very good on customer service and the price aint too bad too. majority of parts are available and they are always breakings cars!!
harlow is technically in essex put its staright down the m25 off at jnct 25 and take ur 1st exit at the roundabout when you come of the slip road and follow signs for harlow...
easy to get to as i travelled there from uxbridge and didnt tk me no more then 45mins.
i dont recall ne1 i knw havin had bad experience with them so i do recommend them but price wise jus giv them a call and see what happens..
btw what are you lookn for for your car?