More from Assistant Commissioner Rowley:

"Having made enormous progress and made some significant arrests and had some significant finds, there still remain important lines of inquiry for us to pursue.

"We've got to try to understand everything we can about the dead terrorist, his associates.

"We need to understand the whole network and how they acquired and built the bomb that exploded on Monday night.

"It's going to take a little more time to close down those gaps in our understanding.

"We are working as fast as we can do because everyone wants answers to this."

"We've got a lot of the risk contained but we still have some uncertainty.

"As we chase down those lines of inquiry we will keep this strong policing presence.

"We need to grow our confidence that we have got every component of the network and we have got as full an understanding as possible about how the device was constructed and whether there's any remaining risk.

"Clearly we haven't covered all the territory we want to but we have covered a large part of it.

"Our confidence has been increasing over recent days but there's still more to do to get to the degree of confidence we want."