More than 100 Muslim leaders have signed a statement pleading with ISIS to release British aid worker Alan Henning.

Mr Henning is currently facing death at the hands of ISIS's British executioner 'Jihadi John' and was paraded before the cameras in a video of fellow hostage David Haines's murder.

Dozens of Imams from around the UK today criticised the terror group as 'monsters' for the brutal murder of Mr Haines and insisted killing Mr Henning would be 'un-Islamic'.

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Alan Henning is being held hostage by ISIS in Syria after he was kidnapped during an aid mission. Muslim leaders in Britain have today condemned the terror group's actions as 'the worst condemnable sin'

The Muslim leaders' letter states: 'We, the undersigned British Muslim Imams, organisations and individuals, wish to express our horror and revulsion at the senseless murder of David Haines and the threat to the life of our fellow British citizen, Alan Henning.'

They said those holding Mr Henning hostage must accept that what they are doing is against the Koran and 'constitutes the worst condemnable sin'.

The letter, published in The Independent, states: 'The un-Islamic fanatics are not acting as Muslims, but as the Prime Minister has said, they are acting as monsters.'

Mustafa Field, director of Faith Forums for London, who helped compile the letter, told the paper: 'This letter shows that British Muslim leaders are not prepared to let these lunatics hijack our faith.'

In another appeal online, Abu Abdullah, representing British Muslim aid workers, told of the various ways Mr Henning had raised money to bring to Syria, having been moved by the plight of people there.

In an emotional speech to the camera Abu Abdullah said: 'You have the ability to spare the life of this innocent man. We beg you to tread the path of justice and show him the compassion that Allah has placed in the hearts of the believers and in your heart.'

The pleas to ISIS came after footage emerged showing Mr Henning's last day of freedom.

The father-of-two, who gave up spending Christmas with his own family in order to carry out charity work in Syria, looks relaxed in the film as he speaks to fellow volunteers - just 24 hours before he was kidnapped by jihadists.

The plea came after a video emrged showing Mr Henning sitting in a Turkish fast food restaurant - just 24 hours before he was captured

The video, which was shown on Channel 4 News yesterday, shows Mr Henning sitting in a Turkish fast food restaurant on Christmas Day as he speaks to six other aid workers who affectionately call him 'Gadget'.

But just hours after he was filmed looking relaxed and happy, Mr Henning, from Eccles, Salford, was snatched by brutal Islamic State militants while attempting to deliver aid.

It emerged this week that ISIS were 'tipped off' about his aid mission to Syria and seized him just half an hour after he entered the country.

The senseless kidnapping, murder and now the despicable threats to Mr Henning at the hands of so-called 'Muslims' cannot be justified anywhere in the Quran. British Muslim leaders today

Security services are now investigating whether ISIS fighters were told about the convoy by corrupt local officials or an insider after it emerged the British taxi driver was seized just 30 minutes after he entered Syria.

The British aid worker was just four miles from the Turkish border when he was taken after militants were reportedly made aware of his arrival.

The day before, he looked relaxed and happy as he shared a meal with six other aid workers.

There is no suggestion that any of the men featured in the new footage were involved in the 'tip-off' that betrayed the father-of-two.

The men spend time praising the work of Mr Henning, who was embarking on his fourth aid convoy into the war-ravaged region.

They describe him as an 'inspiration' and praise his commitment to his work - talking about what a sacrifice he was making spending Christmas there rather than with his own family.

The father-of-two responds by saying that the work he does is 'nothing' compared to what others go through 'on a daily basis'.

One of the men in the video says: 'He could be with his friends and family back home, but he's on his way right now to deliver ambulances and aid to Syria to help our brothers and sisters. Big respect to this guy.'

Affectionate: At one point in the video, one of his fellow aid workers reaches across to hug Mr Henning

Close: Mr Henning, who was filmed on Christmas Day last year, is called 'Gadget' by his colleagues in the video

Another says: 'I just want to say Gadget, you're a soldier, a massive, massive inspiration, you know what I mean.

'People who are not even getting involved in this type of aid work, you know what, don't look at us, look at Gadget… because you know what day it is for him? It's Christmas… It's priceless, I'm telling you it's priceless.'

Another is filmed saying that Mr Henning's actions prove that 'it's not about being Muslim, it's about being human. Doing the right thing, doing the right thing for humanity.'

Mr Henning remains modest and responds to the men's praise, saying: 'It's all worthwhile when you see what is needed actually get to where it needs to go.

'That makes it all worthwhile. No sacrifice we do is nothing compared to what they're going through every day on a daily basis.'

One of Mr Henning's colleagues tonight described the moment he was seized by Islamic State jihadists.

Majid Freeman was on the same convoy in Syria when it was surrounded my masked gunmen.

Mr Freeman, from Leicester, told the BBC that the former taxi driver had been singled out by the jihadists when the convoy was targeted.

British hostage Alan Henning (front row, second from right) may have been captured after ISIS fighters were tipped off about his presence in Syria

He said: 'All these masked gunmen came running into the compound.

'We didn't know what was happening because they weren't speaking English they were speaking Arabic. They were just shouting.

'They tried to find out if we were spies and what our motives were for coming to Syria.

'After this whole ordeal finished and we all came out of our rooms again and those guys went that's when we found out Gadge was actually gone.'

He continued: 'When he held a baby himself in his hand I think that was very powerful for him,' said Mr Freeman. I think that changed his own life.'

Muslim aid worker Pervez Abdullah Rafiq, who travelled with Mr Henning on previous trips to deliver aid to Syria, today issued a video plea to the leader of Islamic State to release him.

In the video Mr Rafiq says: 'Your prisoner Alan Henning travelled with us several times to Syria. On all occasions, we your Muslim brothers, brought him with us under our care and protection.'

He pleads that Mr Henning should not pay 'for the crimes that international governments have committed' with his life.

Mr Henning, pictured (left) on an aid mission last December, was kidnapped shortly after entering Syria

Mr Rafiq recalls how Alan Henning devoted 'all his free time' to raising awareness of the suffering of Syrian children and washed cars to raise money for them.

He also describes how Mr Henning chose to sleep in the van on the journey to Syria rather than pay for a hotel, to avoid spending money that would otherwise go to the people of Syria.

Yesterday it emerged that his fellow volunteers offered his kidnappers hundreds of thousands of pounds to free him.

They had taken the money with them to help Syrian refugees, but decided to use it in an effort to negotiate the taxi driver's release.

But the brutal Islamic State terror group rejected the offered ransom and refused to allow him to return home.

Risks: It also emerged yesterday that Mr Henning was warned by a moderate Muslim of the dangers of entering Syria just weeks before his abduction

Mr Henning was driving an ambulance for Rochdale Aid 4 Syria, which raised money on behalf of Al-Fatiha Global, a British-based organisation which provides humanitarian aid to those caught up in warzones.

It also emerged yesterday that Mr Henning was warned by a moderate Muslim of the dangers of entering Syria just weeks before his abduction.

Mohammed Shafiq, of the Ramadhan Foundation, said he voiced fears that some young Britons wanting to become jihadis had 'tagged along' with aid convoys as a way of joining ISIS.

He said: 'The vast majority of people I know of who've been on the convoys are ordinary law-abiding Muslims who want to help the Syrian people.

'Ninety-five per cent leave the aid at the Syrian border and go home, but of those who go into Syria some may have tagged along in order to join up with ISIS.'

Mr Henning had been on three previous aid convoys to the region and had told friends that he had always felt safe.

Al-Fatiha Global, the charity behind the convoy, is at the centre of investigations by the Charity Commission into claims it had links with people supporting the fighting in Syria.

There is no suggestion Mr Henning knew of the alleged connections between the charity and fighters.

An activist for the Worcester-based charity was allegedly photographed in the summer of 2013 embracing two masked Syrian fighters armed with AK47 weapons.

The Charity Commission launched a statutory inquiry – the highest level of its investigations - into Al-Fatiha Global in March. It is looking at 'serious concerns about the governance and financial management of the charity'.

Al Fatiha Global is run by trustees Michael Lloyd, 70, and Mumtaz Ali, 55, both of Worcester. They declined to comment yesterday.

Questions over Mr Henning's capture came to light as it was revealed that even Al-Qaeda, the terror group behind the September 11 attacks, have pleaded with ISIS for his release.