Second steppers need to find an extra £75,388 to move from a flat to a house, research by online estate agent Housesimple has found.
This is double the step up in price in 2008, which was £37,225.
The report predicted that second steppers may have to find £150,000 to upsize by 2028.
Sam Mitchell, chief executive of Housesimple, said: “While we’re seeing a positive trend with more first-time buyers getting onto the property ladder, Second Steppers – primarily those upsizing from a flat to a terraced or semi-detached house – still face a major jump to transition from a starter home to their family home.
“Despite government commitments to building more stock, family homes remain at a premium. The problem is particularly acute in London and the South of England, where the gap for Second Steppers can feel more like a chasm.
“As a result, Second Steppers migration from London has always been a major driver of house price inflation in commuter towns in the home counties and increasingly as far afield as areas of the south-west.”
In London second steppers need to find a £343,134, followed by St Albans (£218,538) and Cambridge (£181,964)
The smallest difference between the cost of a flat and a house was in Durham (£23,318), followed by Nottingham (£26,561) and Stoke-on-Trent (£27,027).
Mitchell added: “Things look brighter for those living or heading North, where house prices, although on the up, are still in affordable territory.
“And with healthy local economies in northern cities like Leeds, Sheffield, Liverpool and Manchester, the wealth of job opportunities are attracting homeowners who are looking for a fresh start, a better quality of life, and buying a family home is not just a pipe dream.”