Just having a look at Quidco's "Savvy Tips" and I came across this:
"Payday UK Loan have increased their cashback to £70!" - further inspection "£70 for a verified and completed loan"
Interesting, so I had a look at the site - They charge a massive 1335% APR, so you're gonna have to be pretty desperate to take one out but.... look at this page: http://www.paydayuk.co.uk/getting-started/our-charges.html
The minimum you can take out is an £80 loan, which you pay back £100 on your payday (within 30 days) - so thats a £20 charge, but youll get £70 back in cashback, a clear £50 profit.
Quidco doesnt stipulate the amount of loan you need to take out (assuming that they are hoping for repeat business). I might give it a try, its a good a gamble as the ladbrooks deal in my eyes.