The number of thirtysomethings leaving London has leapt in recent years as high housing costs have forced people to move out of the capital, according to campaigners.

Analysis by the group Generation Rent showed that 65,890 people in their 30s moved from London to another part of the UK in 2014-15, a net loss of 30,410 in that age group. This was 48% higher than in 2011-12, when 20,590 more 30 to 39-year-olds moved out than moved in.

Internal migration data from the Office for National Statistics also showed a sharp increase in the number of children leaving the capital. In 2014-15, 26,920 more children under 10 moved out of London than came in, compared with a difference of 19,980 three years previously.

Generation Rent said the exodus had taken place during a period in which house prices in London rose by 37%, compared with 16% in the UK as a whole, and rents increased by 10%, compared with 4% outside London.

It said almost two-thirds of people moving out of London had gone elsewhere in the south-east and the east of England commuter belt, while 12% had moved to the Midlands and 11% to the north of England.

Only among twentysomethings are more people moving into London than out; in 2014-15, there were 37,950 more people in this age group living in the capital than the year before, a 3% increase.

Betsy Dillner, the director of Generation Rent, said: “Growing numbers of Londoners are giving up on the city and its extortionate housing market.

“London is an incredible city and the decision to move away isn’t taken lightly. These people are leaving friends and family in order to find a home they can afford, and some are leaving their jobs. This should worry everyone in London, from employers facing a loss of skills to communities losing valued neighbours, and particularly Sadiq Khan, whose housing policies will need to stop this exodus.”

Research by Lloyds bank found that moving to somewhere an hour’s commute from London could mean paying hundreds of thousands of pounds less for a family home. While the average price of a home in London transport zones one and two was £741,919, in Wellingborough, Northamptonshire, the average was £183,345, while in Peterborough, it was £189,319, Lloyds said.

Andrew Mason, the Lloyds mortgage products director, said: “Commuters to London who don’t mind a longer journey between home and work could reap the financial benefits of living outside of the capital.

“However, the decision of whether to live in the city or further away is not simply a trade-off between financial costs and journey times. Quality of life is also a major factor: family circumstances, better schools, physical environment and homes that offer better value for money also come into the equation.”