£1.7m is a lot of money to deport one person, but in terms of terrorism it is nothing.
I don't even think the murder of Lee Rigby is even worthy of being called a terrorist attack, but I think the massive police operation straight after his death could have easily cost more than £1.7m. I hate to think how much the trial of the two scumbags will cost.
And it's not like the Govt set out to spend so much money. They had to spend that money because of the legal difficulties in shipping him out. If the govt didn't spend that money then he'd still be here.