David Cameron has appealed to former Guantanamo Bay detainee Moazzam Begg to share any information he has about the Islamic State militants behind the capture of Western hostages.
Mr Begg has claimed he offered to help the Government secure the release of British hostage Alan Henning from Islamic State (IS) extremists but was prevented from issuing a direct appeal.
He also said he believed he knew those who held the murdered aid worker and had helped secure the release of hostages from extremists in Syria in the past.
The Prime Minister told BBC's North West Tonight: "We are very happy to to work with anybody. My understanding is that Moazzam Begg did make some appeals, sadly, as we know, those appeals fell on deaf ears. These people in Syria are absolutely brutal and really will stoop to any depths and do the most dreadful and ghastly things, and that is what's happened. But if Moazzam Begg has information to provide about who these people are, he should provide it."
On Tuesday, Mr Begg, 46, who was freed last week after charges of travelling to Syria to support terrorism were dropped, said he made efforts to contact IS militants after Mr Henning's capture and also offered his help later from prison - but this went unheeded.
He criticised the British government because they “abandon their people and try to look tough” while other countries negotiate and get their citizens released when they take hostages.
Mr Henning was murdered last week. He was the second Briton, after aid worker David Haines, to be beheaded on film by IS in recent weeks.
Two US journalists, James Foley and Steven Sotloff, were also killed in the same way.
Mr Begg's comments come as Mr Foley's parents said the policy of never paying ransom or negotiating with terrorists was "basically condemning our own citizens" and denying those taken hostage "the protection of their government".