The scheme would be a financial boon to the hundreds of thousands of families where grandparents are regular childminders, but could lead to widespread fraud.

David Cameron, the party leader, outlined the proposals as he began a charm offensive to woo the grey vote. He accused the Government of being so obsessed with youth that it tried to “airbrush” old people out of society. At the Age Concern conference, he suggested that more recognition should be given to the work of grandparents, who he declared were the “unofficial childminders of Britain”.

“That’s why we’re looking at whether grandparents and other family members should be able to access the money that the Government spends on childcare,” he said.

At the moment, parents get up to £240 a week from the working families tax credit to pay towards approved childcare. However, any blood relatives are automatically excluded as childminders, unless they look after the children neither at their own home nor the child’s home, but at a third location. Mr Cameron believes that the system should be made more flexible, so that parents are paid the childcare allowance even if they chose the grandparents as minders.

At present, the allowance is only available if both parents work more than 16 hours a week and have a joint income of less than £50,000. It is worth a maximum of £140 for one child and £240 for two or more. To prevent fraud, the parents have to prove they are paying the money to the childminders.

Times Recommends

• MPs back creation of human-animal embryos
• Bank Holiday plan to celebrate Armed Forces
• Wanted: criminal law expert to be new DPP