A very worrying development

From the BBC:

Labour is urging the government to explain how a terror suspect under surveillance went missing after changing into a burka at a mosque.

If terror suspects can escape surveillance by changing into a random item of clothing like a burka, then what's to stop them escaping from escaping from jail by changing into a pair of shoes or something which a visitor slips on and smuggles out when they leave?

I blame Harry Potter, so I do.