Single parents in Hammersmith & Fulham are owed £4.85m in child support.
That is according to figures obtained and published by charity Gingerbread, who support single parents, from the House of Commons Library.
The statistics show that £1.97m is owed in Kensington & Chelsea and £3.7m in Cities of London and Westminister.
Fiona Weir, Gingerbread chief executive, said: "We know from single parents that this is much-needed money which pays for items such as children's clothes, school meals, trips and activities and childcare.
"Ultimately the responsibility for paying childcare maintenance rests with the non-resident parent, but the Child Support Agency has to do its job too in collecting debts and enforcing payment."