Well, for those who are interested, I finally had my service at Pro Alfa in Watford.
The whole operation appears to be a 2-man set-up formed by Chris (the manager) and Luis - the guy who actually works on the vehicles.
From the establishment's name I expected the place to be full with Alfas but I then discovered that they work on any vehicle.
My overall impression was very positive. Both Chris and Luis are very young and really friendly chaps and Luis in particular sounds as if he knows what he's talking about. They took time and effort to explain what my service would entail and then went into the details. Nowadays, it's really refreshing to be able to speak to the mechanic working on your car, get advise, suggestions and just chat about cars in a friendly way and that's exactly what the guys at Pro Alfa did.
I was presented with the old parts and filters and I have had the car for 2 weeks now (everything working perfectly), so I have no reason to doubt the work quality.
The place has only been open 6 months and I guess they will need some advertisement if they want to get it known amongst the Alfa owner community. So here is my little contribution with the view to spread the word.
In summary - great people, great prices. Thumbs up from a happy customer.
Iassen from Slough