Any issues with using US bought iPhone 11 in the UK?

I don’t recommend purchasing a US phone to be used in the UK. It’s not that it “won’t work” per se, but there are models specific to your region.

• iPhone 11 Tech Specs US
• iPhone 11 Tech Specs UK

At first glance, the Mobile and Wireless specification for the US lists the A2160 and A2161 models of the iPhone where as the UK version lists the A2215 and A2218 models. Specifically, there are differences in some of the FDD-LTE bands which could affect things like speed or particular service availability.

The best course of action would be to confirm with your carrier as to what the differences of the US vs. the UK models would be in relation to your services.