Last year I got a decent spec Viner Gladius from Halfords, they were retailing for £1350 and got it for £999, it took 8 weeks to arrive from Italy though, but was worth the wait.
This year I wanted a CX/Winter Bike, and the choice was very limited, I must have asked for about 8 different bikes e.g. Focus Mares, Trek Portland, Cotic Roadrat, Genesis Croix De Fer, many brands that they are meant to be stockists for. I eventually got a Voodoo Limba reduced to £699, although I swapped a lot of bits off my old bike.
With the balance of £400 I ordered Disc brakes for my MTB, pedals, and a Mech Disc Brake for my Voodoo, however the service was terrible and in the end I never got the Mech disc.
If you go to another bike shop that accepts the Halfords vouchers, you won't get the extra 10% as that is only available to bikes purchased from Halfords.
Doug