On 15 September 2017, at around 08:20 BST (07:20 UTC), an explosion occurred on a District line train at Parsons Green Underground station, in London, England.

Thirty people were treated in hospital or an urgent care centre, mostly for burn injuries, by a botched, crude "bucket bomb" with a timer containing the explosive chemical TATP.

[4][5][3] Police arrested the main suspect, 18-year-old Iraqi asylum seeker Ahmed Hassan, in a departure area of the Port of Dover the next day, and subsequently raided several addresses, including the foster home of an elderly couple in Sunbury-on-Thames where Hassan lived[6][7][8] following his arrival in the United Kingdom two years earlier claiming to be an asylum seeker.

"[11] A homemade bomb partially exploded on an eastbound District line train at Parsons Green Underground station, in West London.

According to Chip Chapman, former head of Counterterrorism at the Ministry of Defence, "This absolutely didn't function properly because… 1 ounce (30 g) of TATP is enough to blow car doors off".

[24] On 16 September, Kent Police Special Branch arrested Ahmed Hassan at the Port of Dover on suspicion of a terror offence.

[27] Hassan was not named initially, but was identified by media reports as an 18-year-old Iraqi orphan refugee[28] who had been referred to a governmental anti-extremist programme.

The Crown Prosecution Service (CPS) indicated that Hassan had not conveyed his motive for the attack and that, perhaps due to his destruction of electronic devices, there was no evidence of ISIS being an inspiration.

[37] It has been claimed, in an article by Lizzie Dearden of The Independent, that the police missed or misinterpreted evidence indicating Hassan was inspired by ISIS.

I am in close contact with the Metropolitan Police, Transport for London (TfL), Government and other emergency services who are responding at the scene and leading the investigation.

[47] Citing the Parsons Green train bombing, police advised the public not to record terrorist events, but instead to "run, hide, tell".

"[51] On 6 April 2019 it was announced that Lt. Col. Craig Palmer, a passenger on the affected tube train, had been awarded the Queen's Commendation for Bravery for his part in helping to bring the bomber to trial and conviction.

Despite great risk to himself, the Artillery officer, who was two carriages away as the train entered Parsons Green station, went towards the scene of the bomb and recognised it for what it was.