Is my iphone 12 in UK safe to use Or is it causing me to get cancer due to radiation?

According to the World Health Organization, you're fine:

Researchers have conducted a vast number of studies over the last two decades to assess health risks resulting from mobile phones. According to the World Health Organisation, no adverse health effects have so far been established as being caused by mobile phone use.

https://www.reuters.com/technology/apple-disputes-french-findings-says-iphone-12-complies-with-radiation-standards-2023-09-13/

Read this support article for important safety information for iPhone

Important safety information for iPhone - Apple Support

As for the recent stuff in the news, that was something the French government came up with. If you're worried about the radiative energy produced by cellphones (and they all produce some) then get a landline.