LONDON (AFP) - Hundreds gathered for a memorial service for Alan Henning, the British hostage beheaded by the Islamic State in Iraq and Syria (ISIS) terror group, celebrating the aid volunteer as a hero on Sunday.

Friends and family, including his widow Barbara and teenage children Adam and Lucy, attended the ceremony at the Muslim Heritage Centre in Manchester, northwest England.

The 47-year-old taxi driver had travelled to Syria to help Muslim colleagues deliver aid in a convoy. He was kidnapped shortly after crossing the border and his murder was claimed by the ISIS group in a graphic video released on October 3.

Majid Freeman, from the English city of Leicester, travelled to Syria with Henning on two aid convoys, including the December trip on which he was captured.

"He went to Syria to help at a time when the whole international community had abandoned them," Freeman told well-wishers at the memorial service.

He recalled an incident when Henning had declined to join others on the convoy in paying for a hotel for the night, instead sleeping in an ambulance.

"I asked Alan why and he said 'I'm going to stay in my ambulance, I'm going to save that money and give that money to the people in Syria'. That is the kind of person Alan was," Freeman said.

His murder outraged the Muslim community in Britain, moderates and hardliners alike.

A memorial fund for his family has raised more than £25,000 (S$51,700). Henning was the fourth Western hostage murdered by ISIS militants since August.