Iraq-born Tory MP Nadhim Zahawi has said that local leaders in northern Iraq estimate that between 500 and 700 Britons are fighting with the Islamist militants.
He told Channel 4 News that he was seeking further information after a high-ranking official told him one had been found "with a Liverpool Football Club membership card" and another carrying a different UK-related membership card.
A third British jihadi who appeared in an Isis propaganda video was known as Raqib, is 20 years old has links to Leicester, ITV News has learned.
Two other Brits in the video have already been named as Nasser Muthana and Reyaad Khan, both aged 20 and from Cardiff.
Raqib is known to have attended a mosque in Aberdeen. It is believed that Raqib's family moved to Leicester in the last few years.
Ibrahim Alwawi, imam of the Aberdeen Mosque and Islamic Centre, told the BBC: "We, as the Muslim community in the city of Aberdeen, are shocked like everyone else.
"We are co-operating with the authorities as we usually do."
A former friend of the 20-year-old Aberdeen man seen in an Isis propaganda video has told ITV News that the Muslim community in the Scottish town is "devastated" by the revelation.
"We are a close-knit community and the Imam always preaches against this. He always tells - especially the youngsters - to keep away from things like that [becoming involved in extremism]."
Maqbool Chaudry said he had known Raqib for a few years and thought he was "a good kid" before he "moved away about a year-and-a-half ago down south."
"I've been in Aberdeen for over 20 years and I've never ever come across anything like this before," he said.
"That's why the whole community is absolutely devastated and shocked."
Solicitor Simon McKay is representing four of the six families of military policemen who died in Iraq in 2003. He talks about claims of new evidence coming to light that could prompt a fresh inquest into the deaths.
In tonight's documentary on the tenth anniversary of the death of ITV News reporter Terry Lloyd in Iraq, we are given an insight into the family at Christmas.
His daughter Chelsey said her relationship with her father "suffered" during her teens.
Lloyd was killed on the eve of the invasion of Iraq ten years ago.
Who Killed My Dad? The Death of Terry Lloyd airs tonight on ITV at 10.35pm.
A ITV documentary has followed the daughter of ITV News war reporter Terry Lloyd as she retraces his final steps in Iraq as part of her deeply personal search for the truth about the circumstances surrounding his death.
Terry was killed in southern Iraq ten years ago, along with cameraman Frederic Nerac and translator Hussein Osman, after their convoy came under attack by the US Army.
Cameraman Daniel Demoustier - who was driving the vehicle carrying Terry when they were initially fired upon - survived.
Chelsey Lloyd has returned to where he was shot dead, along with Daniel and presenter Mark Austin, who was also in the country covering the start of the war.
“I need an understanding of what happened that day because I wasn’t there and because it was so far away," she said.
"I need to piece together the events of those days to create a kind of timeline, a picture in my head, to help me.”
Who Killed My Dad? The Death of Terry Lloyd is on ITV at 10.35pm tonight.
The mother of a British military policeman killed by a mob in Iraq has launched High Court action in an attempt to force the Ministry of Defence to hold a public inquiry.
Pat Long is seeking a judicial review of Defence Secretary Philip Hammond's refusal to hold the inquiry.
Lance Corporal Tom Keys from Solihull and Corporal Russell Aston from Swadlincote in Derbyshire were part of a group of six Redcaps killed after Iraqis attacked a police station in Southern Iraq in June 2003.
An inquest into the six deaths recorded a narrative verdict of unlawful killing, and said the soldiers should have been better equipped.
Lawyers say a hearing is unlikely to take place until the autumn.