Former colleagues said the kidnapped veteran peacekeeper was a passionate humanitarian who had gone to Syria to help victims of the conflict.
"He really cares about people," said one co-worker in Africa. "He has a good sense of humour."
The hostage's name has been revealed on websites and in news reports around the world, including in England and the US. However, The Herald is respecting the wishes of the family and the Foreign Office not to identify him. There are fears it could inflame the situation.
The Prime Minister David Cameron insisted yesterday Britain will not be cowed by the barbaric murders of the US journalist Steven Sotloff, whose death was featured in a video posted on the internet by ISIS (Islamic State) on Tuesday. It followed last month's beheading by the group of fellow American journalist James Foley. The same killer who speaks with an English accent is seen in both sets of footage..
He said: "Let me be very clear. This country will never give in to terrorism. Our opposition to ISIS will continue at home and abroad."
"I am back," said the masked fanatic, who has been dubbed by the media as 'Jihadi John' who is dressed in black on the video. "Our knife will continue to strike at the necks of your people."
Friends were horrified. The man's capture had been known by those close to him, but not revealed to the public until Tuesday.
The man, who was born in the north of England and raised in Scotland, was working for a European aid agency when he was captured near a refugee camp near Syria's border with Turkey in March 2013. Another European national was taken with him but has subsequently been released. That man said he had been moved frequently before he was freed and he had seen the black flags of ISIS.
International security experts speculated that the man was probably being held somewhere close to the ISIS HQ in the Syrian city of Raqqah. The man, who has previously worked in the military, has served as a security advisor to aid agencies in hotspots around the world. Before going to Syria, he was based in a troubled African country.
A colleague said: "At this time, we can confirm that he worked for us in 2012. He was not working for us at the time of his abduction. We join with the rest of the world in hoping for his safe release."
The married man was based in a country in the Balkans where he had business interests and a family. He was educated in Scotland and also has a brother and a sister north of the Border.
After chairing a meeting of Cobra, the Whitehall emergencies committee yesterday, the Prime Minister denounced the beheading of Mr Sotloff, from Miami, as "sickening and brutal" and said he felt "shock and anger that it again appears to have been carried out by a British citizen."
Mr Cameron, who is now at a two-day Nato summit in Wales, told MPs: "The only way to defeat it is to stand firm and to send a very straightforward message: a country like ours will not be cowed by these barbaric killers. If they think that we will weaken in the face of their threats, they are wrong; it will have the opposite effect. We will be more forthright in the defence of the values -liberty under the rule of law, freedom, democracy - that we hold dear, and I'm sure a united message to that effect will go forward from this House today."
Philip Hammond, the Foreign Secretary, made clear the Government would look at "every possible option" to protect the British hostage threatened with death by ISIS extremists.
He admitted senior ministers had been aware of the latest hostage for some time. He said: "I can assure you that we will look at every possible option to protect this person."