As the title says,
A free £5 Amazon credit will be applied to your account when you set a visa debit/credit card as your default payment.
I already had a visa card as a default payment on my account, but that didn't prevent me from claiming the offer. I simply just clicked the card that was already on my account and the £5 was credited straight away.
It'll be a case of some accounts are eligible and some aren't, so just click the link to see if you're one of the lucky ones.