The UK is a sovereign nation and absolutely can enforce its laws against anyone within its borders, regardless of citizenship.
The only potential exception is diplomatic immunity, and that is only granted to the few people who are directly employed to represent a foreign nation. (And even then, such immunity is voluntarily granted by the UK government.)
The only potential exception is diplomatic immunity, and that is only granted to the few people who are directly employed to represent a foreign nation. (And even then, such immunity is voluntarily granted by the UK government.)