Is this because of a storage subscription? If so, can you turn off iCloud photos, choose keep originals, set up the UK subscription storage and then re-enable iCloud photo? Or transfer them temporarily to a laptop or desktop storage and then upload them again later.
Personally, I did not know that subscription storage couldn’t be transferred from one country’s subscription rate to another. So if that’s the cause, I would definitely suggest transferring them to a computer anyway for safe keeping - buy an external drive if needed, but back them up somewhere independently no matter what.
Transfer photos and videos from your iPhone, iPad, or iPod touch - Apple Support
and Get help with iCloud Photos - Apple Support
“If you have Optimize Storage turned on, you might not have all of your original photos and videos on your device. To download the original photos and videos on your iOS device, go to Settings > [your name] > iCloud > Photos and select Download and Keep Originals. On your Mac, open Photos, choose Photos > Preferences, then select Download Originals to this Mac. Then you can turn off iCloud Photos. You can also select the photos and videos that you want to download from iCloud.com.”