I trust you were typing that^ when I posted mine but I'll address the points you raise.
1. some 13 year olds can look like 18 year olds[i Yes, they can. It is a statement not an excuse.
[i]2. He married the victim] This takes him out of the 'sex-tourist' bracket because he entered into a (wrong but legal in Bangladesh) long-term relationship; very different from Glitter.
[i]3. He may not be a British National (though he’s been a teacher in UK for several years so I'd be surprised if he isn't.[i] A suspicion on your part does not make it so; he needs to return to Bngladesh regardless.
4. The law was not in force until 2008, but they were together till 2009. Obviously they did not have sex after the law cam in effect in 2008, right oh! If the girl was in Bangladesh and he was teaching in UK there may not have been any sexual contact between them. In any case, I hope that if there *is* something that he can be prosecuted with, he is.
Although, with a foreign national committing a 'legal act in a foreign country' in that country, I don't see why we should pay for a prosecution.....