I've a different view of Halfords, strangely enough. Very good service and experience, but probably a one off.
Halfords Tottenham Hale has an enthusiastic mechanic working there called Dan, nice guy, and very good. He trued a wheel for me recently, brilliant job done!
Every other job he has done has been great.
The only problem is that his MTB bike knowledge extends to mostly modern trash, (though he has and does repair and service everything from Rod braked Roadsters to Racers) and his knowledge on materials is naiive to say the least (for instance, he knows nothing about what Phil Wood is and actually thinks Titanium is more brittle than Aluminium)
But I understand that most Halfords are pretty crap, in regards Cars as well as Bikes.
My halfords days are over now, as they charge too much, my LBS does it quicker for less dosh and while I wait