There are no European csc codes for US firmware. You should get 4G but not 5G in the UK. You will need to change the APN settings to those of your provider, however, your device may be region locked which means purchasing an American sim and making a 5 minute phone call. Also, be warned, you have no warranty.
The US version supports most 4G bands in the UK (with the exception of band 32 that Vodafone and Three use) so you should still get 4G as Pugs says you should get 4G but not 5G as the US model doesn't support N78 or N28