MPs from all the main parties have urged the Government to act “without delay” on its pledge on protecting child refugees, after it emerged that children as young as 10 were enduring freezing temperatures sleeping rough across Europe.

In a letter to Home Secretary Amber Rudd, the 150 signatories – including 54 MPs, 61 Lords, as well as bishops, councillors and NGOs – ask that all 480 places promised for unaccompanied minors under the Dubs Amendment are filled before the end of the year.

Family reunions for lone children with family in Britain should be accelerated, they said, adding that youngsters who are currently waiting many months to access this legal route are often falling into the hands of smugglers and traffickers.

The renewed appeal comes after the first unaccompanied child stranded in Greece arrived in the UK – a year and a half after the Home Office pledged to bring hundreds to safety. The Home Office had accepted that the boy was vulnerable and eligible for transfer 16 months ago.

During the demolition of the Calais “Jungle” in October 2016, the UK gave sanctuary to 200 children under the Dubs provision. But since then, no children have been transferred from the north of France under the legislation.

This is despite the fact that there are an estimated 100 lone minors currently sleeping rough in Calais. Volunteers working on the ground say one of them, an unaccompanied Afghan boy, is just 10-years-old, and is currently sleeping between two trees.

With an onslaught of freezing temperatures last week and pressure from charities, the authorities in Calais opened sheltered accommodation in a warehouse with capacity for a total of 270 people. But with between 600 and 700 refugees in the area, many are still having to sleep outside in the rain and snow.

Refugees in Calais have been enduring freezing temperatures, some suffering hyperthermia (Futuro Berg/Help Refugees)

Annie Gavrilescu, who is working on the ground in Calais with charity Help Refugees, which also signed the letter to Ms Rudd, told The Independent: “It’s really, really freezing. There’s a lot of snow and rain. It’s not the nice kind of snow; it’s bitter cold and miserable.

“People don’t sleep very much in the night. It’s impossible – it’s too cold and wet. And then they’ve also got police often coming and removing any makeshift shelters they’ve made. We’re seeing signs of hyperthermia – people are very pale, sometimes they have slurred speech and get very faint.

“You can definitely sense how the mood has gone down even further. It’s just really desperate and despondent. We’ve always said we want the places filled by the time this big freeze comes. It’s now here, and kids as young as 10 are having to sleep outside.”

The letter says: “In light of the current detrimental situation in Calais, a continued commitment by our Government to its legal obligation to fulfil the Dubs Amendment appears to be more important than ever.

“The previous transfer of 200 children in 2016 proves that our Home Office and our Government are able and willing to follow a proud tradition of being a safe haven for child refugees. Knowing that at least four children lost their lives last year at our border in Calais before the Amendment was implemented is heartbreaking, and we cannot let this happen again.

“We are writing to ask that you ensure further safe transfers to the UK as swiftly as possible to fill the 480 capacity, and to urge the Government to provide swift access to family reunion so that children do not have to risk their lives to reach protection and their families.”

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The letter also urges that the EU-Turkey deal eligibility deadline of 20 March 2016 be reconsidered, as currently only children who arrived in Europe before this date are considered eligible under Dubs – meaning many who arrived more recently are not being considered for the scheme.

Involvement in anti-exploitation and anti-trafficking efforts in northern France must also be renewed and reinforced, the signatories state, claiming the UK has a duty to safeguard refugees from the dangers posed by exploitative criminal networks before they reach Britain.

Recent research by Refugee Rights Data Project indicates that the majority of child refugees in Calais are facing sustained and increasingly brutal forms of police violence as well as abuse by civilians, with many also suffering from untreated mental and physical health problems.

The Independent revealed earlier this year that refugees in the region had been subject to aggressive use of tear gas and repeated destruction of possessions at the hands of local police, whose conduct was recently condemned by the French government following an independent inquiry.

The growing desperation of displaced children, many of whom have family members in the UK, has made them increasingly prone to exploitation at the hands of smugglers and traffickers, who are said to promise them a free crossing in return for “work” upon arrival in the UK.

Responding to the letter, a Home Office spokesperson said: “We remain committed to transferring 480 children from Europe to the UK under section 67 of the Immigration Act.

“We have accepted further referrals this year and transfers are ongoing. We will continue to work closely with EU partners and local authorities to transfer eligible children here quickly and safely.