AFAIK there aren't any really good cashback cards in the UK at the moment. You can get 0.5% with either Tandem or Aqua. I have the latter because I didn't have 3 years of UK address history when I moved back.
Fact is you're better off using a 'stoozing' card and putting what you WOULD be paying into whatever high interest account you can find. Eg, even though it's reduced, you can still get 3% on £1500 with TSB - and if you have a partner, that can be two single and one joint account. There is Nationwide FlexDirect which pays 5% for the first year. And so on.
Nothing like the US or Canada, but then the interchange fees are capped in the EU, so there just isn't the headroom for large bonuses or cashback.
You can, at least, get an Amazon voucher on signing up for the Aqua card I believe. I got £20.