Abu Rumaysah has grand plans for Britain – and specifically 10 Downing Street, home to the prime minister of the United Kingdom.

The British man suspected of being the masked militant in the latest Islamic State execution video explains what he would change at the iconic London address: “These are the black flags of Islam. This one’s actually the flag of the Islamic State,” Rumaysah says as he rummages around his garage in Walthamstow, East London. “One day when the Sharia comes, you will see this black flag fly over the Downing Street.”

Rumaysah appears in a Channel 4 documentary that was aired on January 19, called The Jihadis Next Door. Its director, Jamie Roberts, said he had the “chills” when he heard the voice in a recent ISIS propaganda video, because had and his fellow filmmakers have been following Rumaysah and his associates for years.

Roberts’s documentary follows extremist preachers in the UK who, while gleefully sponging off government handouts, have gone on record with their radical plot to establish Muslim rule in Britain. The two focused on also happen to be known associates of Rumaysah, who is also known as Siddhartha Dhar or ‘Jihadi Sid’.

The documentary delves into their grand ambitions, from holding public executions on the Ealing Common in West London. arresting Prime Minister David Cameron and Chancellor George Osborne for crimes against Islam and even visions of an even cushier life on benefits under their new Islamic overlords.

“That would involve me sitting there practising Islam the way I want to practice it and getting paid – getting my JSA without having to sign on,” says one of the preachers, Abu Haleema, who is also seen giggling with his friends as they watch the latest ISIS propaganda videos.

Filmed over two years, the documentary also attempts to give some insight into clashes between the extremist preachers, who want to see Sharia rule Britain, and moderate British Muslims who reject their philosophy.