Apparently, border police let him in despite his trip to Libya, Syria and return back to Manchester via Turkey and then Dusseldorf.
I would simply refuse entry to such people or bring them in for questioning and then send them back.
I can't imagine what justification this terrorist tit would have had for those trips. We must tighten up our border controls, customs and rules for entry that's for sure.
No argument on this. Although he was British-born, I think its reasonable to ask him to provide verification for what he was doing in states like Libya and Syria. British passport or not.
But the government have given up on trying to control movement across our borders. As I understand it, and I'm happy to be corrected, if you're awaiting rights of entry and residence in the UK at present, you will be released into the community until a decision is made. If you're refused, you will only be deported if you are arrested for another crime, nobody comes looking. Why would they? That would be seen as a waste of budget. These people have disappeared from whatever was their declared address by that time anyway.