The US and UK governments are failing to support Iraqi Christians, leaving them vulnerable to be squeezed out of their homes, MPs have said.

Iraqi Christians who fled after their homes were overridden by ISIS are at risk of being pushed out the Middle East altogether by a combination of Shia and Sunni forces moving in, they warn.

In a letter to the British development secretary Priti Patel, several MPs alongside charity heads and religious freedom campaigners say unless funding is immediately provided to rebuild Christian villages and homes on Iraq's Nineveh Plains, 'most Iraqi Christians who escaped ISIS to Kurdistan are likely to leave Iraq permanently'.

Signed by the Catholic peer Lord Alton as well as Labour's faith envoy Stephen Timms and Second Church Estates Commissioner Dame Caroline Spelman alongside others, the letter says: 'We note that DFID were able to allocate significant emergency funds for the support of residents from Mosul, and the rebuilding of the same, but nothing has been allocated to date for the many thousands of Christians and Yazidis who lost their homes 3 years ago (including in Mosul) and who are now faced with a grave humanitarian and existential crisis.'

They point to a memo claiming: 'In many of these towns, Iranian-funded Shia populations have made clear their desire to move into historically Christian towns and lands. Likewise, Sunni voices have indicated that "abandoned" Christian lands and homes should be utilized to house displaced Muslims from Mosul. Other rival militias and political fronts, many from outside the area, are also staking unfounded claims to these lands.'

The memo warns it is now or never, saying unless 'substantive progress' is made in the next 45 days, other groups will move in and claim the land.

Thousands of Christians, Yazidis and other religious minorities were forced from their homes when ISIS swept through northern Iraq.

More than 30,000 now want to return to their devastated towns on the Nineveh Plains, according to a briefing from Stephen Rasche, a director for the Chaldean Catholic Archdiocese of Erbil's relief programme.

But American and British funding is directed through the UN which is being funnelled to support rebuilding Mosul with virtually none set aside for the Christian communities across the rest of northern Iraq.

'Timely and targeted US assistance would have an immediate impact in facilitating the return of Christian IDPs [internally displaced peoples] and boosting the confidence of the broader Christian IDP population in their ability to resettle in the Nineveh Plains,' says Rasche.

He points to an American bill known as HR 390 – the Iraq and Syria Genocide Emergency Relief and Accountability Act – which he says is 'critical' and 'would authorize and direct the kind of assistance that could immediately improve conditions on the ground and demonstrate US leadership'.

Rasche goes on: 'The delivery of US assistance, as authorized and directed in HR 390, would make a time-sensitive and historical contribution to the future of Christianity in the Middle East. This tangible display of US leadership could also spur urgent action from other potential donors such as the UK and EU.'