Chris and Roberta Hodder recently moved from Forest Hill in Lewisham to Eastbourne in Sussex with their children, aged six and 11.
They told BBC London that for them it was the prospect of never being able to own a house that drove them out of London.
Their former three-bed rented property has now sold for £600,000 as they settle by the seaside in a house the same size they bought for £200,000.
“As we were planning to leave, we noticed quite a few kids disappear off the books at our local primary. While visiting a house in another coastal town, there was a couple next to us who were also planning to move out of the city; it definitely seemed like the trend around us,” Mr Hodder, a lobbyist, explained.
“Long term, we need security for our family. I don’t think it’s healthy that London is becoming a city without children – it’s becoming a necropolis.”