A poll of 2,000 people by the Telegraph found just 30 per cent want it to remain.
A number of MPs are now calling for a rethink following the Brexit vote.
Tearfund's advocacy officer Paul Cook told Premier's News Hour it's vital the commitment remains.
He said: "We are in tough times but we shouldn't be turning off the tap to the world's poorest.
"It's only 7p out of every £10 that the government spends and it's having a huge impact on some of the very poorest people in our world."
"That money saves someone's life every two minutes."
The commitment was enshrined in law during the coalition government after pressure from the UN, charities and campaigners.
After resigning as Prime Minister, David Cameron said it was one of his greatest achievements.
Paul Cook called on Christians to remember the significance of this money.
"As Christians we have to follow Jesus' instruction to love our neighbour and care for the poorest," he said. "This is an amazing way in which the UK can be doing this and we as Christians can be continuing to support the government as they do this."
A spokesman for the International Development Department said: "As an outward-looking, globally engaged nation, we believe that the UK should work to tackle international problems at their source - not wait for them to arrive on our doorstep.
"The aid budget makes us stronger in the world, and we are determined to use it to secure our national interest as well as help the world's poorest."
Listen to Paul Cook speaking to Premier's Marcus Jones on the News Hour: