More young graduates in London now live with their parents than on their own because they are unable to afford the cost of renting or buying a home, while those from outside the capital are finding themselves locked out of the city altogether.

Research by the Sutton Trust undertaken with the London School of Economics found that 15 per cent of graduates aged under 35 live with their parents, compared with only 11 per cent who live alone.

Meanwhile poorer graduates who aren’t originally from London are finding it increasingly difficult to move to the capital as a result of high – and rising – housing costs, marking a serious threat to social mobility.

Sir Peter Lampl, chairman of the Sutton Trust education charity, said: “The Sutton Trust has helped thousands of young people from low and middle income backgrounds to study at some of our best universities over the last 18 years. But during that period it has become increasingly difficult for those with good degrees to afford to move to London.

“This matters to social mobility because so many of our leading jobs in finance, politics and policy and the professions are based in the capital. Increasingly, as the evidence presented in this new report shows, it is clear that getting less advantaged young people to good universities is only half the battle – they need to be able to access the best jobs after graduation.”

The research said that only 6 per cent of new graduates who move to London come from the most disadvantaged fifth of UK local authorities, compared to the 42 per cent that come from the most advantaged fifth of UK local authorities. Fewer than 20 per cent of graduates moving to London come from outside the South.

Graduates from poorer backgrounds were found to be affected to almost the same extent as those without any higher education.

While London has always attracted high levels of migration, in the past this was offset by older residents leaving. This traditional outflow has decreased, reducing supply of housing stock.

Population rises outstripped the rate of building of new homes by three per cent between 2001 and 2011, a disparity that has increased in the past four years.

Bexley and Barking and Dagenham are now the only two London boroughs where average house prices are less than eight times the average income according to the research.

The report also criticised the Conservative’s Help to Buy scheme for adding as much to demand as to supply, and called for more innovative solutions to the problem.

Four types of scheme were suggested with the potential to alleviate London’s housing crisis for young graduates: student-style housing; modular, pre-fab homes; enforced planning regulations for new dwellings to remain in the private rented sector for a set number of years; and age-targeted developments offering smaller sleeping accommodation with a pay off in quality social space and good locations.