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.
1345 The situation thus far: it's unclear what the nature of these incidents is. But it is clear there have been several, scattered around London. In the last few minutes the tube has, just as it was two weeks ago to the day, been closed down. A London Ambulance spokesman has told PA they were called to Oval at 12.38pm and Warren Street at 12.45pm. There are no details of the alert at Shepherd's Bush yet. There are no reports of casualties at any of the scenes.
Meanwhile, a bus in the east end of London, on Hackney Road, has been cordoned off, and the area evacuated.
1335 There have been reports of gunshots at Warren Street, but these may have been detonators going off, Scotland Yard is suggesting. There is another report of a nail bomb at Warren Street.
1333 Emergency services are now said to be responding to an incident on a bus in Hackney Road, in East London.
1328 PA reports: "A Scotland Yard spokeswoman said: 'Emergency services personnel are responding to reports of incidents at three locations on the Underground - the Oval, Warren Street and Shepherd's Bush.' Police were also among those attending the three stations, she said.
She could not confirm reports that witnesses at Warren Street had seen smoke." There are no reports of any injuries.
1315 We're getting new reports of a "series of incidents" on the tube network. Warren Street, Oval and Shepherd's Bush tubes have all been evacuated, and emergency services are attending. Services on the Victoria, Northern and Hammersmith & City line have been suspended.
Sky News is reporting a minor explosion on one tube at 1254. An eyewitness claims one passenger's backpack blew apart, but did not cause further damage. There was panic on the train, but passengers were able to disembark.
