UK police are investigating a Christian charity to determine if it financed terrorism after its chairman was involved in the freeing of 226 hostages held by ISIS in Syria in 2016.

The Assyrian Church of the East Relief Organisation (Acero) is chaired by the bishop of Syria, Mar Afram Athneil, but is run by Andy Darmoo, 71, who is the director of a lighting company in southern England.

In its financial statements for the year ended July 31, 2016, Acero has an expenditure of £147,689 (Dh682,000) marked as "Iraq Hostages". An Associated Press report in 2016 described Mr Athneil as being "almost exclusively" behind the year-long brokering of the deal to free the hostages. Three were murdered on camera by ISIS.

The exact ransom amount is unknown but is estimated to be in the millions.

Related: Timeline of ISIS in Iraq
Related: Attacks on Assyrians in Syria By ISIS and Other Muslim Groups

"In January 2018, the Met received a referral from the Charities Commission over concerns relating to alleged payments to Syria by" Acero, a statement by London's metropolitan police said.

"This matter is being investigated by officers from the National Terrorism Financial Investigation Unit (NTFIU), which is part of the Met's Counter Terrorism Command, to determine if terrorist financing offences have been committed," it said.

Police said officers executed search warrants at a residential address and business in the Dartford area in Kent and interviewed under caution an unidentified 71-year-old man.

But Mr Athneil has insisted the charity was not involved in the hostage rescue.

"As a bishop in the Assyrian Church, my responsibility was to look after my flock in my country during a troubled period. This had nothing to do with Acero UK or Mr Andy Darmoo. What happened in this situation is between me and my God," he said in a letter to The Sunday Times, who first reported the news.

Mr Darmoo said the £147,689 was sent to Iraq as humanitarian relief after the hostages were freed and that the reference in the accounts was a mistake.

The UK Charity Commission said they were unhappy with his explanations and were worried about the "perception of a link between the charity and a payment of funds to a terrorist organisation holding the hostages caused by the involvement of the chair of the charity in securing the release of the hostages," The Sunday Times said.

The investigation is ongoing and Mr Darmoo has insisted he did not send any money to Syria.