Unless someone corrects me does not need to be main dealer for your BMW warranty just as long as all genuine BMW Parts are used.
So if you are in Surrey I would recommend Munich Legends I get mine done there and if there is any Warranty work which does require Main Dealer they work with Vines of Gatwick ( or they did when I used them

).
and two other good points they will be cheaper than the stealer especially for a Insp2 (I just paid around 770) for mine and usually some very nice cars in the showroom to have a look at
Just for peace of mind
http://www.munichlegends.co.uk/bmw-servicing-south-east