Police operations 'come into open'

Analysis By Mark Urban BBC security correspondent

The spotlight has been thrown onto high-profile police operations in the aftermath of Thursday's failed attempts to detonate three bombs on London tube trains and one on a bus.

We have really seen something coming forward that we might have suspected was lurking beneath the surface in London, and has now come out into the open.

Heavily-armed police and surveillance squads ready to swoop - and all this started with the Harrow Road exercise on Friday.

We can speculate about the kind of effect that giving someone a warning might have, if you suspect they might be a suicide bomber Second man held over bomb alert

There were officers in plain clothes and with assault rifles - something with much more stopping power than the uniformed man has got, which is just a 9mm weapon.

Assault rifles are not the kind of things one would normally see in London.

Also, as they entered the address at Harrow Road, we saw not only assault weapons and flak jackets, but also respirators in case of the use of tear gas.

However, I don't think that raid produced much.

But when they later went back to Stockwell and raided there, that was a much more productive exercise. That is where a man was arrested.

Secret rules

The police rules of engagement have also changed.

This type of exercise that has been carried out by police in recent years is code-named Operation Kratos.

It consists of trying to learn the lessons of all the situations round the world where people have tried to stop suicide bombing before.

Armed police are operating under Operation Kratos guidelines

In the past two years, firearms and surveillance units of the police have been retrained in new procedures under the Kratos rubric, and these include changes to the rules of engagement.

There are also changes to the way you might put someone under surveillance.

We can speculate about the kind of effect that giving someone a warning might have, if you suspect they might be a suicide bomber.

We can speculate about whether the police aim differently but we don't know, because those rules of engagement are secret.