RBS, which owns Natwest, said the change of policy is being introduced primarily to “address the inflationary pressures being seen in London” and will be applied in addition to the standard affordability assessment.

Lloyds Bank introduced a similar measure at the end of May.

The clampdown by the two state-backed lenders comes as the Bank of England is considering tightening controls on risky mortgage lending.

As house price growth in London and the South East hits 18 per cent last month, figures confirm the majority-uptake of the Help to Buy scheme has been in the north. However, calls to rein in the Help to Buy scheme from the European Commission and UK politicians continue to get louder.

Yesterday, Nationwide reported May house prices rose to the boom time-high hit in October 2007. UK house prices increased by 0.7 per cent in May and were 11.1 per cent higher than May 2013, in what was the 13th consecutive increase for the UK.