It would be not surprising to have less legal protections for your privacy as foreign citizen abroad. Not sure about UK law, but take as example the FISA Amendments Act of 2008 in the US:
PS: Note that some believe that's the reason the UK is so hell-bent on data collection. The theory is that the US have stronger legal protections against collecting data of their own citizens but less protections about accessing citizens' data collected by an allied country...