(REUTERS) - This boy is featured in the latest Islamic State (ISIS) video, saying: "Go kill the disbelievers right over there" in English.

He's been recognised by British man Sunday Dare.

"He's my grandson. I can't disown him. He's my grandson, I know him very well," said Mr Dare.

His daughter, Grace Dare, is a woman from London who left Britain to join ISIS and marry a militant.

"She should come back and face the music, because she has let herself down," Mr Dare added.

The video, which could not be independently verified by Reuters, also showed the killing of five men accused of spying for Britain.

A masked man, also speaking in a British accent, threatened Prime Minister David Cameron and vowed that ISIS would one day occupy Britain.

Mr Cameron has said the video is "desperate" propaganda from an organisation that is losing ground.

In November, British officials said that up to 800 Britons had travelled to Iraq and Syria, some to join ISIS.