[.eXe]

I've bought a Corsair H115i but it doesn't fit in my current case (I knew this before a bought it), so I'm looking for another. A full tower case would be preferable but not necessary. It also needs to be able to hold a Rog Strix 5700 XT graphics card as well as the 280mm radiator.

My budget is about £100, it's not a lot but I would appreciate any recommendations.

[Egregious]

NZXT H510. Supports your 280mm radiator mounted in the front of the case. With the radiator mounted there, you'll have 325mm of GPU clearance. Your graphics card is 305mm in length so it'll fit. The price is well within your budget.
https://www.nzxt.com/products/h510-matte-white

[.eXe]

A little over your budget but this case is just perfect. Mesh front panel for maximum airflow along with 3 fans.
https://www.amazon.co.uk/Phanteks-PH-EC5...B088T3VMKK

A little over budget but I can make that work pretty easy I think. Thanks Sam!

[Defector]

I've bought a Corsair H115i but it doesn't fit in my current case (I knew this before a bought it), so I'm looking for another. A full tower case would be preferable but not necessary. It also needs to be able to hold a Rog Strix 5700 XT graphics card as well as the 280mm radiator.

My budget is about £100, it's not a lot but I would appreciate any recommendations.

I can vouch for Phantek. My current case is a Phantek Enthoo Pro ATX Full. It's quite roomy and the glass side panel has me like 😎