The National Union of Teachers, which carried out the survey, said living in the capital is no longer a sustainable, long-term option for teachers.

The union is urging the victor in May’s mayoral election to address the problem and avoid a teacher shortage “crisis” that will hit every school and college in London.

Christine Blower, NUT general secretary, said: “It cannot be rational to allow new teachers to be squeezed out of London, while at the same time, the city needs 100,000 extra school places before 2020.”

She added: “The next mayor and London Assembly must urgently tackle housing costs, support the building of new schools, and not only value teachers but fight their corner.”

Three fifths of the 1,200 young, London-based teachers surveyed said they could not see themselves still teaching in the city in five years’ time.

Most of them pointed to the cost of living as the reason they planned to leave.

The average monthly take-home pay of a newly qualified teacher is £1,600, while the average monthly cost of renting a one-bed flat is now over £1,100 - and rising - according to the NUT.

More than half of young teachers surveyed were renting privately and 18 per cent were living with parents; many had little expectation of getting on the property ladder.

Many complained of being forced into unsuitable housing with high rents and unscrupulous landlords.

Housing has been a hot political issue during the mayoral campaign, with both Labour candidate Sadiq Khan and Conservative Zac Goldsmith pledging to give Londoners priority over new homes.

Ahead of the London elections on 5 May, the NUT is calling for the next mayor and London Assembly to:

• Advocate for rent controls and more affordable housing in London, with investment for councils to build homes, so that parents and children are not priced out of their communities.
• Take urgent action to provide affordable housing to enable London schools to keep the teachers they need.