The bomb at Parsons Green appears to be similar to those used in the terror attacks in London 12 years ago, according to a bomb disposal expert who played a key role in the emergency response to those atrocities.
Major Chris Hunter, who sat in meetings of the Cobra emergency response committee following the terror attacks on July 7 and July 21, 2005, spoke to talkRADIO after this morning's explosion on a District Line train at Parsons Green.
The incident is being treated as terrorism. Photos from the scene appear to show a white tub with wires, inside a shopping bag.
Hunter, a former counter-terrorist bomb disposal specialist in Iraq, told Jon Holmes: "When I saw the train today it was exactly the same sort of picture that I saw when I was in Cobra on 21/7."
The bomb "was crude in terms of its component parts" but "it shows a level of sophistication" and "is very dangerous to manufacture."
He explained: "The upside for us is that after not very long at all it desensitises.
"If I was going to put my money on it I would say it was a failed high-explosive device where the initiator didn’t go [off] and [those who were there are] all very, very lucky."
He also explained the reason there might have been a timer in the device is because "they might put a back-up timer in there - they might put a back-up radio control initiation if the person [meant to detonate the device] bottles it."
Hunter said one positive from this morning's events is "we’ve got a gold mine of forensics biometrics and intelligence there."
Listen to the full interview above