It can’t prevent it, but if they do, it could forbid them from selling stuff in the UK, fine their UK branch, jail their personnel, arrest Tim Cook when he sets foot on UK soil, send out a request to arrest him to Interpol, even (but that’s not likely) send their marines to Cupertino to arrest Apple’s entire management team (cf
https://en.wikipedia.org/wiki/American_Service-Members%27_Pr... for an example where a country legalized invading a friendly country under certain circumstances)
That could be enough of a deterrent for Apple.