For those asking about Amazon 5 monthly payments thing, you can check if your account is eligible here:
https://www.amazon.co.uk/b?ie=UTF8&node=14805641031
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To be eligible for this offer, you must reside in the United Kingdom, your Amazon.co.uk account must have been active for at least one year, you must have a valid credit card associated with your Amazon.co.uk account, and you must have a good payment history on Amazon.co.uk."
The term credit card applies to debit cards as well.
Personally, I've used this in the past but missed a £6 payment due to having to replace my debit card so I think that is why my account was not eligible. I signed into a family member's account and theirs was eligible so placed the order there.