Everything I’ve heard about the B’Twin Triban in that price range is excellent. But might I also suggest getting an older ‘higher end’ bike?
Last spring, I bought a 2005 Trek 1200 for £200, and it has served me brilliantly. I eventually put new wheels on it, but otherwise hardly spent any other money upgrading, and will continue to use it as a winter bike now that I have ‘moved on’.
If I was you, I would be looking both at the B’Twin and keeping my eye on ebay for something even higher spec, but older. I have personally had a lot of good luck with Trek bikes, but just find something you like the look of with at least Shimano 105 on it, and you’ll be fine.