Cashback network Rakuten is now in the UK! "Each time you make a purchase with one of our partner shops via Rakuten.co.uk or using the browser extension, they pay us a commission. We then share this with you as cashback. Simple as that!"
Get £15 bonus cashback at Rakuten when you sign up using referral code: https://friends.platform.rakuten.eu/friends?invite=HDNPRZPF
Eligibility requirements - you need to spend £20 with one of their retailers within 30 days of signing up. So, essentially, you can get a £20 spend for £5. Nice!
(The referee gets £15 per successful referral.)