as well as DNA samples, every one convicted of a crime and deported should first be anesthetised and tagged like they do with dogs.. in several places.. so that they can't just dig them all out..
then each port of entry to the UK should be fitted with scanners built like the metal detectors..and the police should be equiped with hand held scanners...
that way they would be flagged up instantly if they tried to come back in with a fake pasport, or could be checked if stopped by police..