Andy_M wrote:The lower end GT, specialized and Trek bikes (or Boardman for that matter) are far from mediocre, there is very little that you couldn't ride on them, it just might take you a bit longer.
They're all acceptable, but none of them are anything special. If you want a bike that is notably better than what you have now, spend more money.
I think something like an Orange P7 or a Rocky Mountain Blizzard would be nice; you'll not get change from £1000 for a new one, but you'd get a really good secondhand one for less than half that.
If you want something at the level of a new £500 bike, just get some slightly better parts for the bike you have now.