For a couple of years, I've been using WAD near Wolverhampton. They're an independant and the work and prices are better than a dealer. The only downside is that 'cause it's such a small place, you don't get a courtesy car.
Their number is 01902 401711. The proprieter, Willie, is well respected in Alfa circles and regularly features in the AROC mag. He and his brother also set up (if memory serves...) the first Alfa dealer in the Midlands, many years ago.
By the way, where do you live - I've noticed a couple of 155's spring up where I live in Streetly - I say a blue 155 at my local gym (David Lloyd, Great Barr) and a red one with a St. Georges cross on the bottom of the bootlid near the Queslett Pub, Streetly - either of them you?
There's always one - and it's usually me!