The masked man in an Islamic State of Iraq and the Levant (ISIL) video showing the killing of five men accused of being Western spies is believed to be a Londoner known as "Sid" who was associated with hard-line groups.
Siddhartha Dhar - who left Britain for Syria while on police bail after his arrest on suspicion of belonging to a banned group and encouraging terrorism - has been identified by UK media as the spokesman in ISIL's latest death film.
The video also featured a young boy wearing a black bandanna around his head and camouflage clothing, threatening in English to "kill the kaffir [unbelievers] over there".
Sunday Dare, a Londoner of Nigerian origin, identified the child as his four-year-old grandson, Isa. Dare told British media his daughter - who grew up a devout Christian named Grace before converting to Islam and changing her name to Khadijah - had taken London-born Isa to Syria with her to join ISIL.
| Media outlets identify 'Jihadi John'
The latest execution video revived memories of "Jihadi John", another British ISIL member who appeared in several videos in which hostages were killed. He was believed to have been killed in a US air strike late last year.
A convert from Hinduism who lived in east London, Dhar regularly attended protests staged by the now-banned organisation al-Muhajiroun, and had often spoken to the media in support of radical causes.
Since leaving Britain, Dhar - who once sold inflatable bouncy castles - gained further attention through online videos in which he extolled life under ISIL.
Khadijah Dare is also a keen propagandist for the group who has posted images of herself and her toddler son pointing rifles on social media.
How Iraq recaptured Ramadi and why it matters
Meanwhile, a spokesman of the US-led coalition said on Tuesday that ISIL's territory shrank by 40 percent from its maximum expansion in Iraq and by 20 percent in Syria in 2015, as international forces pushed its fighters out of several cities.
ISIL in 2014 swept through one-third of Iraq seizing Mosul, the largest city in the north, and reaching the vicinity of the capital Baghdad. But in recent weeks Iraqi troops have made gains.
In Syria, ISIL is fighting the army of President Bashar al-Assad and other rebel groups opposed to his rule. It is facing air strikes by the US-led coalition and by Russia, which has sent warplanes to support the Syrian government.
| Coalition confident 2016 will bring successes against ISIL