The BBC has confronted a neo-Nazi in Finland who shared online instructions on how to commit arson with UK rioters during the summer.

The 20-year-old was an administrator in the Southport Wake Up group on the Telegram messaging app, where he was known as “Mr AG”. He posted the arson manual, which was pinned to the top of the group chat.

In late July and early August, the group was key in helping to organise and provoke protests that turned to violence in England and Northern Ireland.

We tracked Mr AG – whose real name is Charles-Emmanuel Mikko Rasanen – to an apartment on the outskirts of the Finnish capital, Helsinki.

It was from here, more than 1,000 miles away from Southport, that the neo-Nazi took a prominent online role during the UK riots.

On 29 July, within hours of the killings of three young girls at a Taylor Swift-themed dance class in Southport, the Southport Wake Up group was created.

Within days it had grown to more than 14,000 members. Mr Rasanen – or Mr AG as he was known online – helped to run the group chat.

The group organised the very first protest in the UK, on St Luke’s Road in Southport, the day after the killings. That protest later turned into a riot.

Before the group was taken down by Telegram, a series of other protest locations were advertised, as well as a list of dozens of refugee centres, suggested as potential targets.

Alongside that list, Mr AG posted the arson manual, writing: “Something fun for you to read.”

The manual is believed to have been written by a Russian fascist group proscribed as terrorists in their own country.

It includes details on how to avoid the police and it encourages the targeting of Muslims and Jews.

Underneath the post, other members wrote aggressive and offensive comments, including: “I’m ready for these migrant boys,” while another describes “invaders” as “a stupid bunch underestimating whites”.

Mr AG pinned the post to the top of the group, which meant it was in full view of all 14,000 members when they logged in.

At the time, several riots had broken out across the UK.

The BBC travelled to Finland to confront Mr Rasanen – we had previously emailed him. He refused to answer any of our questions, but did not deny sending the posts or being an administrator of the Southport Wake Up group.

Before we left him, he also accused the BBC of harassment and rang the police.

On his Telegram accounts, Mr Rasanen celebrates Hitler and promotes a neo-Nazi group called the Nordic Resistance Movement, which is banned as a terrorist organisation in several countries, including the US.

He also posts voice notes – in one he describes himself as a “national socialist”, and in another he appears to call for the genocide of Jewish people.

Veli-Pekka Hämäläinen, an investigative journalist at Yle, Finland’s national broadcaster, says Mr Rasanen has been active online “for many years”.

Mr Hämäläinen’s team has also spoken to him about his role in the UK riots. He believes Mr Rasanen’s involvement in the Southport Wake Up group transformed him from a solitary extremist into someone with an audience of thousands.

“This is an example of how lone internet keyboard warriors can turn dangerous,” says Mr Hämäläinen.

He says he has seen Finnish police records, which show Mr Rasanen was investigated when he was a teenager for making an illegal threat, but that he has never been charged with a crime.

The BBC has also been told of Mr Rasanen’s previous online links to a far-right white nationalist group in the UK, Patriotic Alternative (PA).

He was an active member of a private gaming group chat, and his posts were shared by key figures in PA, according to the British anti-fascist research group, Red Flare.

These included the group’s Yorkshire regional organiser, Sam Melia, who was jailed earlier this year for inciting racial hatred.

During the time of the UK riots, a post by Mr AG read: “When is the same violence coming to Northern Europe?”

A spokesperson for Red Flare – which first identified Mr AG’s real identity and his links to Southport Wake Up – says Mr Rasanen should be held accountable for what he has done.

“What we have here is a case of a young man sitting behind his keyboard in a different country starting racist violence in Britain,” they say. “It exposes the transnational nature of the far-right in the world today.”

The BBC contacted Patriotic Alternative, and although the group refused to answer specific questions, it did say what Mr AG posted on PA’s public channel was “fine” and that PA was not involved in what Mr AG posted in other Telegram groups.

Speaking to the BBC, the government’s independent reviewer of terrorism legislation, Jonathan Hall KC, says “if [Mr Rasanen] was in the UK he would be arrested and prosecuted under the 2006 Terrorism Act”.

Mr Hall estimates at least half of terrorism propaganda prosecutions last year involved the Telegram app.

The UK has no extradition agreement with Finland, and the Home Office has declined to comment on whether any extradition request or other action is being taken in respect of the matter. The BBC is not aware of any arrest warrant being issued.

The National Police Board of Finland says it is “aware of the matter”, but it is not possible to comment in more detail.

A spokesperson for Telegram has told the BBC its moderators removed UK channels calling for violence when they were discovered in August, including Southport Wake Up.

Its statement adds: “Of course, we are ready to co-operate with both the UK and Finnish governments on this matter through the appropriate channels.”

A spokesperson for the UK government says it is working at pace to implement the Online Safety Act, which requires social media platforms to remove illegal content and prevent the spread of misinformation.

“We will not let the internet serve as a haven for those seeking to sow division in our communities,” says the spokesperson.

Additional reporting by Rebecca Wearn, Erika Benke, Phillip Edwards & Shayan Sardarizadeh