Far-right material which radicalised Finsbury Park attacker Darren Osborne is "unpalatable" but difficult to police, a senior counter-terrorism officer has warned.

While the internet played a significant role in fuelling the 48-year-old's "hate-filled agenda", much of the content he accessed "doesn't cross the threshold" to be considered a criminal or terrorist offence, commander Dean Haydon, of the Metropolitan Police, said.

He also cautioned that someone could access extreme material and carry out at an attack just hours later due to the speed of radicalisation, as he called on internet companies to do more to tackle dangerous content.

Mr Haydon, head of Scotland Yard's counter terrorism command, said: "We have to be alive to the fact that people are accessing this material and they are using it to self-radicalise, and that's what happened in this case."

He added: "Yes, there's material as I said that's unpalatable, not particularly pleasant, but it doesn't cross the threshold in relation to either a crime or a terrorism offence - and that's really difficult for us then to police.

"It is out there, people can access it and - as we've seen in this case - it certainly affected Osborne in the way it did and certainly played a key part in his radicalisation."

The trial heard how Osborne became "obsessed" with far-right material online in the lead-up to the June 19 attack.

Devices found at his home showed frequent internet searches for English Defence League founder Tommy Robinson and Britain First's Jayda Fransen and Paul Golding.

Mr Haydon declined to call EDL's Mr Robinson a "radicaliser", but said: "There is material out there linked to some of the groups connected to him that quite clearly has been an influencer in this case."

It is believed it took just three to four weeks for Osborne to develop extreme views and decide to hire a van, which Mr Haydon said demonstrated "that individuals can become radicalised really, really quickly".

He said: "To be honest, some individuals could look at material today and decide to go and do an attack later on this evening.

"Some of this material is easily accessible, so we have to look at the role of the internet."

Three far-right groups - National Action, NS131 and Scottish Dawn - have been proscribed in the UK since 2016, and arrests over domestic extremism have increased.

Mr Haydon, who described the far-right as an "emerging threat", said: "We are committed to tackling all forms of extremism including this particular aspect."

By Sally Wardle