They should have followed up Omar Khyam's contact with Mohammed Siddique Khan!
No, they shouldn't have. In the case of yesterday's traitors, they did what they could with the resources they had available to them.
And a damn fine job they did as well.
In a society that believes healthcare comes out of nowhere but has to be free at the point of use; that believes it's morally acceptable for women who've aborted their own children to be supported in their old age by the children of others; that consistently places the un-natural on a par with the natural (a society where 16 year olds can leave school without qualifications and no intention to work and then be given money screwed from the pockets of others cannot last - it is ahistoric, meaning it has no place in history); perhaps those people who have to work to a budget could always do better.
But on the other hand MI5 is not permitted to rattle collecting tins outside Brent Cross, so for the most part they have to make what I'm sure are sometimes split second decisions about where, when and how the resources they have to work with should be allocated to achieve the best possible result. In such circumstances they become pure economists, constantly evaluating how the resources they have can be allocated most efficiently.
You can have a National Health Service or real security, but you can't have both. You can have a welfare state or real security, but you can't have both. You can have a bloated aid budget or real security - but you can't have both.
And anyone who says you can, or who seeks to second guess the work the security services do, is unworthy of consideration.
Good work, folks. Keep it up.