Little bit outside of Norwich in East Dereham, but only 15 miles is MB Autocentre (MB Auto Centre | Mercedes Service & Repair Specialist Centre). Have used them for the last 3 years and only had good experiences. Mainly servicing, but when I did have a fault that needed fixing they bent over backwards to fit it in and get it done. Place looks a bit chaotic, but don't let that put you off.
Did look at Merc Pro but Chose MB Autocentre as it is more convenient for me.
Just Had My C220 Serviced B, MERC PRO in Wymondham Norfolk Fantastic experience. An honest Good Independent Garage. Richard is a great MB Mechanic and did more than required, And ended my nightmares over Timing chains when he told that my car was post that era and no worries PHEW!!!
So I will return for next service there highly reccommeded