Alerts around London

1532 We are waiting for the start of Tony Blair's statement. We'll continue with our coverage of this afternoon's events in new posts here on Newsblog and on our front page.

1526Things remain tense around central London. Sky News reports that University College Hospital has issued an internal memo asking them to look out for a black, possibly Asian man, around 6ft 2ins tall, with wires protruding from a hole in his blue top. The hospital has been cordoned off. (1930 Update: the hospital says a memo was sent round - but the details, as reported by Sky News, are just rumours. Police say the hospital seige is "entirely unconnected" to the terrorist attacks). Meanwhile, we've just seen pictures of a man being escorted away by armed police officers from the gates at the end of Downing Street.

1445 PA reports: "The whole of Shepherd's Bush Green is cordoned off between Holland Park and the Shepherd's Bush Station". There are suggestions there is a suspect package there.

1440 It is now becoming clear that there were three attempted bombings today - at Oval station, at Warren Street station, and on a 26 bus in Hackney. Speculation suggests the detonators on these devices went off, but the bombs themselves did not. Should this be the case, there are clearly going to be huge risks in disarming the devices. But in the bombs there is the potential for clues as to who, exactly, is behind this.

1431 Sir Ian Blair, Metropolitan Police commissioner, says there are four scenes of explosions, or attempts at explosions. He says "casualty numbers are very low" and the devices are smaller than last time. The tube is closed down "for a short while", although mainline trains are running normally. The Cobra committee is about to meet.

1430 Newsblog reader Robert Andrews notes possibly the first moblogged pictures and video from one of the scenes.

1411 Police have now closed off University College Hospital, near Warren Street. This was the place where many of the injured from the July 7 attacks were treated. There were reports earlier that someone had run off after leaving a bag at Warren Street.

1400 An eyewitness has told Sky News that he was in the carriage next to the explosion at Warren Street. Someone dumped a large, black holdall or rucksack on the train and then ran off. Other passengers tried to stop him running away, but he escaped. Something in the bag went off, making a sound "like a Champagne cork popping".

1351 It is now being reported that there was an attempted suicide bombing at Warren Street, but the bomb didn't go off properly. Some windows were blown out of the number 26 bus at Hackney, it is reported, although images from a helicopter above the scene show little damage. Scotland Yard says it is not treating this as a major incident, yet - this does not appear to be on the same scale as July 7.