After four deadly terrorist attacks in the UK this year, Friday morning’s incident at Parsons Green Tube station, in Fulham in west London, was relatively minor in terms of casualties. Nobody was killed, and although 29 people were treated in hospital none of their injuries is believed to be serious.
The bomb, packed into a builder's bucket and left on a District Line train inside a Lidl supermarket bag, appears to have been poorly assembled and failed to detonate. The explosion was strong enough to create a fireball, which caused the flash burns that accounted for most of the injuries, but not sufficient to make a bigger blast.
Had the device been a little better designed it could have killed or injured everyone in the carriage, which was packed with commuters, parents and children shortly after 8am. The stampede that followed the explosion, as the train emptied into a single staircase at the station, is evidence of the panic any attack on the transport system is likely to cause.
The attacks at Manchester Arena, Westminster Bridge, London Bridge and Finsbury Park were deadly and unpredictable. But nothing is likely to strike fear into Londoners, who take terrorism in their stride, like the threat of an attack on the Underground. Within hours of the Parsons Green attack part of King's Cross station was evacuated as police investigated a suspicious package.
The design of the Parsons Green device was similar to those used in four failed attacks in London on July 21st, 2005, two weeks after the 7/7 attacks on the Underground and buses killed 52 people. The July 21st bombs were packed into buckets at three Underground stations and on a bus, but only their detonators exploded.
The remains of the device at Parsons Green could be a rich source of evidence for the police, who have also been examining CCTV recordings from all the stations the train stopped at on its journey. By Friday evening, however, the suspect was still at large, and potentially capable of carrying out a second attack.
Theresa May, the British prime minister, criticised as "unhelpful" a tweet from President Donald Trump, which suggested that the suspect had already come to the attention of UK authorities. It was unclear last night if Trump's tweet was based on a US intelligence report or was nothing more than his own uninformed speculation.
A number of those alleged to have been behind the other terrorist attacks in the UK this year were already known to intelligence agencies, which are monitoring 3,000 radical Islamists and a smaller number of far-right radicals.
The mayor of London, Sadiq Khan, on Friday called for more police resources, prompting the prime minister to defend her government's record in protecting police budgets. During the general-election campaign earlier this year Labour used the terrorist attacks to draw attention to the Conservatives' cuts to police numbers.
Labour's shadow home secretary, Diane Abbott, avoided politicising the Parsons Green attack on Friday, but with the party-conference season about to begin that restraint is unlikely to last for long.