DAC Clarke said documents were found at the bomb scenes

It is now nearly a week since more than 50 people were murdered and several hundred injured in an appalling terrorist attack here in London.

Innocent people going about their daily lives, be it as tourists, working, or simply living here as residents have been affected.

From that moment on, as the Commissioner declared last week, police have worked painstakingly to put together every shred of evidence we could to mount what we want to be a successful investigation.

No-one should be in any doubt the work last Thursday is that of extremists and criminals Asst Cmssr Andy Hayman

I'd like to thank at this juncture the support of everyone. The media, the communities and those trying to live, work and visit London. Their patience has been a very important ingredient to get where we are now.

To give us all some idea of what the team have been working through I would like to describe some of the activity we've been engaged in.

Several hundred witness statements have already been taken, over 1,000 actions have been raised, many of them prompted by some very useful and constructive calls from the public to our Anti-Terrorist Hotline.

Doesn't that say an awful lot about our communities here in London and across the UK?

In addition, we have seized and started to view more than 2,500 CCTV tapes, and these are being urgently viewed for obvious reasons.

I would now like to ask DAC Peter Clarke, head of the Met's Anti-Terrorist Branch, to update you on today's developments in the investigation.

As you are obviously all aware we are conducting a complex and intensive terrorist investigation. I can tell you that this investigation is moving at great speed.

The investigation led us to have concerns about the movements and activities of four men, three of whom came from the West Yorkshire area.

We are trying to establish their movements in the run up to last week's attacks, and specifically to establish if they all died in the explosions.

Today we executed six search warrants issued under the Terrorism Act at premises in the West Yorkshire area.

As and when we find areas where the public can be of specific help, we will of course give more information and ask for their help Dep Asst Cmssr Peter Clarke

These included the home addresses of three of the four men to whom I have referred. A detailed forensic examination will now follow. This is likely to take some time to complete.

We have identified CCTV footage showing the four men at King's Cross station shortly before 8.30am on that morning of July 7.

One of the men who set out from West Yorkshire was reported missing by his family to the Central Casualty Bureau shortly after 10pm on Thursday, July 7. We have now established that he was joined on his journey to London by three other men.

We have since found personal documents bearing the names of three of those four men close to the seats of three of the explosions.

As regards the man who was reported missing, some of his property was found on the Route 30 bus in Tavistock Square.

Property in the name of a second man was found at the scene of the Aldgate bomb. And in relation to a third man property in his name was found at the scene of both the Aldgate and the Edgware Road bombs.

We also have very strong forensic and other evidence, that it is very likely one of the men from West Yorkshire died in the explosion at Aldgate. This, of course, is subject to formal confirmation by the Coroner.

The investigation is still in its early stages. As and when we find areas where the public can be of specific help, we will of course give more information and ask for their help, which we know will be forthcoming.

However, I would like at this stage to thank the public for all the support and assistance they have already provided. It is invaluable.

At one of the searches in West Yorkshire, some material has been found which has caused the West Yorkshire police to take measures to ensure that there is no risk to the public.

The investigation of what has been found will be a detailed and lengthy exercise.

At Luton a vehicle has been found in the station car park which we suspect is connected to this investigation. Again, steps are being taken to ensure that there is no risk to the public.

One man has been arrested in West Yorkshire and will be brought to London to be questioned.

I am sure you will understand that in this fast moving and very complex situation, it would not be appropriate for me to answer questions about other aspects of the investigation.

My absolute priority is the safety of the public. We will give you further information as and when it's possible in the future.

I understand that times like these can be very difficult for our communities. There is a need to be reassuring and ask for calm.

The excellent relationship the police service right across the UK enjoys with our communities will be there to support, encourage and reassure.

I said only a couple of days ago that it is at times like these that communities bind together.

I want to conclude by making it absolutely clear that no-one should be in any doubt the work last Thursday is that of extremists and criminals.