It seems counter-intuitive but forget about Halfords now.I did do a hell of a lot of research and the general consensus was that it was a better bike than the Giant Escape 1 I was looking at. Halfords was the only thing people warned of and the setup isn't actually that good. One gear won't work and I've got a strange squeak when I push down hard on the left pedal. But I'm glad I went for the better bike and the local bike shops will surely get my custom when I need a good service or repair!
The missing gear is just a simple indexing problem (hopefully), which your LBS will soon sort, whilst bad mouthing Halfords.
The left pedal is probably a simple set up issue so the same applies.
Don't leave it though, esp the gears, as it will 'wear' unevenly.