An extra 3,000 unaccompanied children may be accepted into Britain after a number of Conservative MPs are rumoured to vote against the government in a crucial vote on Monday evening.

The home secretary Theresa May has announced her opposition to the move and has reiterated the government's pledge to take an extra 3,000 children from camps around Syria.

However she may be overruled when the House of Commons vote tonight on an amendment to the Immigration Bill tabled by the Labour peer Lord Dubs. If passed it would allow 3,000 child refugees in camps around Calais and Europe in to the UK.

The Christian leader of the Liberal Democrat party, Tim Farron, has been a long-time advocate of the plans, which are also supported by Save the Children. He told the BBC's Andrew Marr show the government's promise to take an extra 3,000 children from camps around Syria was not enough.

Farron estimated there were 30,000 lone refugee children in camps in Europe who were vulnerable to trafficking and abuse.

"I've been to the camps, I've seen families absolutely devastated, people who've fled war and persecution, the threat of death for them and their children and they took an enormously risky decision to cross the water the come to Europe. Why? Because what they left behind was riskier still," he said.

He added: "My question to every Conservative MP, to Theresa May and to David Cameron, is, 'If you were in the situation of these Syrian refugees, if your children were like these unaccompanied children in Europe now, what would you want other countries to do for you?' The answer is obvious."

Krish Kandiah, founder and director of Home for Good, a Christian adoption and fostering charity, said it was time for Christians to act quickly.

He told Christian Today: "This is a vital vote that will determine the safety of some of our world's most vulnerable children.

"I urge you to tweet your MP or email them to encourage them to back Lord Dubs amendment."

Theresa May said the government had put in £10m to help and support for refugee children who are in Europe. The government's refugee resettlement programme has solely targeted those in camps in Syria and surrounding countries, not those in Europe.

Dubs' amendment has had a parliamentary device known as "financial priviledge" attached to it. This means if it is defeated by the Commons on Monday evening, it cannot be tabled again in the House of Lords.

Yvette Cooper, chair of Labour's taskforce on refugees, said the application of financial privilege to the amendment was "an appalling thing" to do. "It shows they know they have lost the moral argument," she said.