SIR – After every terrorist attack somebody pops up a few days later and says “Well, actually we did know about these people before and that they posed a threat”.

What use is that? I’ve got a lot of respect for the intelligence services. They do a brilliant job. We owe them a lot but surely after doing all the hard work of pinpointing these people surely the easy bit would be to at least keep an eye on them.

They seem to think they’ve done enough by working out that they exist.

I know every human being can’t be monitored 24 hours a day on the off-chance they might get up one morning and decide to kill a load of people, but surely they can keep an eye on the ones they know are a threat.

Simon Halliday, Taunton Street, Shipley