Elderly relatives and grown-up children of refugees resettled in Britain are being severed from their families under UK asylum rules, the Red Cross has warned.

Asylum rules on family reunion currently mean refugees who are granted asylum in the UK can only bring children under 18 and spouses with them, and will affect the 20,000 Syrian refugees due to arrive in the UK in the next five years.

Ministers are now under mounting pressure to reform the rules, potentially opening the doors to thousands more vulnerable Syrians.

Labour’s Yvette Cooper and Liberal Democrat leader Tim Farron are among MPs backing an amendment to the Government’s Immigration Bill, which goes before MPs on 1 December, which would see the right of reunion extended to successful asylum seekers’ dependent parents and grandparents, children over 18 and in some cases siblings.

MPs backing the amendment have pointed to harrowing cases, highlighted by the British Red Cross, of families torn apart by existing asylum rules. In one case two Syrian brothers have been unable to bring their mother to the UK, leaving her alone and without any family support in a refugee camp in Iraq.

Yvette Cooper, chair of Labour’s refugee taskforce, backs the amendment to the Immigration Bill (Getty)

In another, a family with three daughters have had to leave the eldest, who is 19, behind in Syria at the mercy of trafficking gangs and with no legal route to join her family.

Although it is thought unlikely to pass in the Commons tomorrow, there are hopes the amendment to the Immigration Bill could succeed in the House of Lords, where the Government lacks a majority.

If the amendment is passed, it could potentially open the doors to thousands more Syrian refugees, above and beyond the 20,000 the Government has pledged to resettle by 2020. However, the Home Office declined to speculate on the Government’s response to any change in the law ahead of the debate on 1 December.

The 20,000 Syrians currently due to arrive includes family members of original applicants who are permitted to join them under the current rules.

Ms Cooper, chair of Labour’s refugee taskforce, said that asylum rules in both Britain and Europe were not working.

Refugees settle in Germany Show all 12 1 /12 Refugees settle in Germany Refugees settle in Germany Germany Mohamed Zayat, a refugee from Syria, plays with his daughter Ranim, who is nearly 3, in the one room they and Mohamed's wife Laloosh call home at an asylum-seekers' shelter in Vossberg village on October 9, 2015 in Letschin, Germany. The Zayats arrived approximately two months ago after trekking through Turkey, Greece and the Balkans and are now waiting for local authorities to process their asylum application, after which they will be allowed to live independently and settle elsewhere in Germany. Approximately 60 asylum-seekers, mostly from Syria, Chechnya and Somalia, live at the Vossberg shelter, which is run by the Arbeiter-Samariter Bund (ASB) charity 2015 Getty Images Refugees settle in Germany Germany A refugee child Amnat Musayeva points to a star with her photo and name that decorates the door to her classroom as teacher Martina Fischer looks on at the local kindergarten Amnat and her siblings attend on October 9, 2015 in Letschin, Germany. The children live with their family at an asylum-seekers' shelter in nearby Vossberg village and are waiting for local authorities to process their asylum applications. Approximately 60 asylum-seekers, mostly from Syria, Chechnya and Somalia, live at the Vossberg shelter, which is run by the Arbeiter-Samariter Bund (ASB) charity Getty Images Refugees settle in Germany Germany Kurdish Syrian asylum-applicant Mohamed Ali Hussein (R), 19, and fellow applicant Autur, from Latvia, load benches onto a truckbed while performing community service, for which they receive a small allowance, in Wilhelmsaue village on October 9, 2015 near Letschin, Germany. Mohamed and Autur live at an asylum-applicants' shelter in nearby Vossberg village. Approximately 60 asylum-seekers, mostly from Syria, Chechnya and Somalia, live at the Vossberg shelter, which is run by the Arbeiter-Samariter Bund (ASB) charity Getty Images Refugees settle in Germany Germany Mohamed Ali Hussein ((L), 19, and his cousin Sinjar Hussein, 34, sweep leaves at a cemetery in Gieshof village, for which they receive a small allowance, near Letschin Getty Images Refugees settle in Germany Germany Mohamed Zayat, a refugee from Syria, looks among donated clothing in the basement of the asylum-seekers' shelter that is home to Mohamed, his wife Laloosh and their daughter Ranim as residents' laundry dries behind in Vossberg village on October 9, 2015 in Letschin, Germany. The Zayats arrived approximately two months ago after trekking through Turkey, Greece and the Balkans and are now waiting for local authorities to process their asylum application, after which they will be allowed to live independently and settle elsewhere in Germany Getty Images Refugees settle in Germany Germany Asya Sugaipova (L), Mohza Mukayeva and Khadra Zhukova prepare food in the communal kitchen at the asylum-seekers' shelter that is their home in Vossberg village in Letschin Getty Images Refugees settle in Germany Germany Efrah Abdullahi Ahmed looks down from the communal kitchen window at her daughter Sumaya, 10, who had just returned from school, at the asylum-seekers' shelter that is their home in Vossberg Getty Images Refugees settle in Germany Germany Asylum-applicants, including Syrians Mohamed Ali Hussein (C-R, in black jacket) and Fadi Almasalmeh (C), return from grocery shopping with other refugees to the asylum-applicants' shelter that is their home in Vossberg village in Letschin Getty Images Refugees settle in Germany Germany Mohamed Zayat (2nd from L), a refugee from Syria, smokes a cigarette after shopping for groceries with his daughter Ranim, who is nearly 3, and fellow-Syrian refugees Mohamed Ali Hussein (C) and Fadi Almasalmeh (L) at a local supermarket on October 9, 2015 in Letschin, Germany. All of them live at an asylum-seekers' shelter in nearby Vossberg village and are waiting for local authorities to process their asylum applications, after which they will be allowed to live independently and settle elsewhere in Germany 2015 Getty Images Refugees settle in Germany Germany Kurdish Syrian refugees Leila, 9, carries her sister Avin, 1, in the backyard at the asylum-seekers' shelter that is home to them and their family in Vossberg village in Letschin Getty Images Refugees settle in Germany Germany Somali refugees and husband and wife Said Ahmed Gure (R) and Ayaan Gure pose with their infant son Muzammili, who was born in Germany, in the room they share at an asylum-seekers' shelter in Vossberg village on October 9, 2015 in Letschin, Germany. Approximately 60 asylum-seekers, mostly from Syria, Chechnya and Somalia, live at the Vossberg shelter, which is run by the Arbeiter-Samariter Bund (ASB) charity, and are waiting for authorities to process their application for asylum 2015 Getty Images Refugees settle in Germany Germany German Chancellor Angela Merkel pauses for a selfie with a refugee after she visited the AWO Refugium Askanierring shelter for refugees in Berlin Getty Images

“I have met refugee parents separated from their children or orphaned young people whose siblings are in the UK, whilst they are stuck in refugee camps,” she said. “We should be doing more to allow families who have been driven from their homes by war, violence and persecution to be reunited in a place of sanctuary.

“As the winter closes in and we start turning our attention to Christmas, I hope the Government will take action to support those refugee families who have been torn apart by conflict to be reunited.”

Mr Farron said existing reunion rules were “far too narrow” and called on Conservative MPs to back the amendment, which is also supported by the SNP and the Green Party.

“When you are fleeing for your life and making a journey to safety you can become separated from your family. The government recognises that families who find themselves in this situation deserve to be reunited, which is why there are reunion rules already in place,” he said.

“This is just one part of what we should be doing to help those in crisis and is something that any reasonable Conservative should accept as the right thing to do.”

Alex Fraser, head of refugee services at the British Red Cross, said the charity had helped reunite 300 refugee families this year, but encountered numerous cases obstructed by the current rules.