The Brits don't care to live.
It might be useful to keep this particularly virulent nest open. After all, you can watch who goes in and out and know that these people are much more likely to be involved in terrorist attacks than people on average. It gives you leads.
Unless your idea was just to incinerate the place druing prayers. That might kill some terrorists, but it would also kill some relatively innocent people. It would be frowned upon by most people.