Immigration Status
All the people defending the police and immigration services' behaviour are missing the point. Yes, the police had a right, or even duty, to hand stuff over to the immigration services, if they thought there was something relevant - but this isn't what happened.
Here's a thing: ALL arrests of non-British Nationals under terrorist legislation are automatically red flagged to the immigration services with a view to deportation. And they would indeed investigate "the possibility that he had been less than truthful in his application to stay." And then, the home office decides to use an emergency deportation so as to circumvent the necessity of having a hearing, which kinda implies that they didn't find anything in their investigation that would stand up at one.
What this shows is the extent to which you can be tarred by accusation in this country, for both terrorism and immigration. The fact that they tried to rush him out of the country without a hearing should obviously show that he hasn't done anything. But mention scare words like "terrorism" and "immigration" or both together and everyone stops thinking.