I have 2 Carrera road bikes, Vanquish and TDF LTD, both bought second hand. Try to go for the ones with the carbon forks and 2x8 speed or 2x9 speed gears
The large sized 54cm frame weight with carbon forks is about 2kg, the steel forked models will be heavier.
With some upgraded bits you can get the bike weight to 10kg
The good thing about Carrera bikes is they are usually an impulse buy and purchasers lose interest in cycling quickly, which means you can often pick them up with less than 50 miles on the clock.
Assembly is not the best, very little grease on anything. If they get left out in the rain things will rust up quickly.
An hour with a tube of grease and a bottle of bike oil is time well spent.
If you're patient you can pick any of the Carrera bikes up for about £100 in almost new condition. I have paid as little as £70 , on an
ebay auction ending at a silly time of day, for a like new Zelos, which I flipped for £120
Consider the Subway or Parva for a city bike, the MTBs seem to be a bit more desirable, but the road bikes and hybrids are less so.