Former Archbishop of Canterbury, Lord Dr Rowan Williams, has criticised the Government for being "very slow" in its response to the refugee crisis and said it has "little to show" after pledging to reunite families separated by conflict.
Lord Dr Williams joined more than 200 religious leaders to call on Theresa May to do more help refugees fleeing Syria, Iraq and other war zones.
Speaking at the Liberal Jewish Synagogue, he said that together the different communities were proposing an "opening up of our (the UK's) current conventions and protocols" to speed up the reunion of families separated by war.
They called for visa processes to be "relaxed" so that refugee families living in the UK can be joined by relatives stranded abroad.
Lord Dr Williams' intervention comes as more than 200 Christian, Muslim and Jewish clerics, alongside lead representatives of other faiths, signed an open letter urging Mrs May to unblock rules preventing refugee families being reunited in the UK.
"Under the present immigration rules, a British doctor of Syrian origin could not bring her parents from a refugee camp in Lebanon - even though they were refugees and she could support and house them," the letter says.
"A Syrian child who arrived alone in the UK could not bring his parents from a refugee camp in Jordan - even if the child were recognised a refugee and even though his parents were themselves refugees.
"Families in these situations can currently be reunited only by resorting to desperately unsafe irregular journeys, sometimes ending in avoidable tragedies."
Their letter follows similar calls from around 300 top former judges and lawyers, approximately 120 of the world's senior economists, and 27 charities and NGOs.
The government recently announced that it had secured enough local authority places to meet its pledge to resettle 20,000 Syrian refugees over the next four years.
And in a major U-turn earlier this year, former prime minister David Cameron committed to accepting 3,000 unaccompanied children registered in France, Italy and Greece.
A spokesperson for the Prime Minister said that more than 120 unaccompanied children have come to the UK from Europe since the start of the year, and more than 30 since the Immigration Act was passed in May.
They added that the current system "already allows for reunification.
"So if the UNHCR recognises an individual somewhere else in the world as a refugee and they have family ties to the UK, then their asylum claim will be processed and they can be resettled here."
"The system is broken and the Home Office must establish a functional system which delivers now, without bureaucratic delays," he said.
"At the current rate of reunification, it will take a year before all the children in Calais are reunited with their families.
"This is forcing children to take matters into their own hands on rail tracks, stowing away in lorries and putting themselves into the hands of unscrupulous people traffickers. How can a civilised country allow this to continue?"
Last week, the US and Russia agreed on a plan to try to end the civil war in Syria.
Rebel groups in Syria said they would accept the planned ceasefire, which is due to start on Monday.