I've used Steve at Brownchurch for many years with my previous 110 TD5, and initially with my L322 5.0 S/C, until they moved locations.
They were based in Leyton, so very convenient from Canary Wharf, but this year moved out to Essex on the M25 border. Not far away, but I just couldn't make that work with dropping a car off and getting back to the office, so after being with Steve for 13 years had to look for someone else this year. I highly recommend Brownchurch though if you could get there - they've been superb with me over many years, nothing was ever too much trouble, and they really knew their stuff.
I went with LRR Range Rovers in Greenwich this year for a routine service. I obviously don't yet have much experience with them, but seemed very competent and knowledgeable, so I'd certainly use again. I was going to take it back there to replace both my front air springs when one sprung a leak, but ended up doing it myself.
QP Online also seems to get good reviews and be very active, and used to have a place in Barking, although I'm unclear if they still have that, or are now Maidstone only.