The mayor of London could backtrack on his policy that 50% of housing redevelopment after the Olympics should be affordable, amid claims of a £1bn “black hole” in land values.

Neale Coleman, an adviser to the mayor, said at a culture, media and sport select committee hearing that he was “in discussions” with the Olympic boroughs about reducing the requirement for affordable housing. He was responding to claims that falling land values are likely to see the National Lottery lose all the £2.4bn contributed to the Games.

However he rejected claims that sale of the land would only raise £800m, £1bn less than estimated, and not enough to pay back the National Lottery’s contribution to buying land.

The pledge to build 50% affordable housing, as well as being a requirement under the mayor’s London Plan, was a specific commitment in the bid that won the Games.

Coleman also said the 44% requirement for family housing was under discussion.

The Olympic boroughs have long been concerned that regeneration would be sacrificed by the need to raise money to pay back the Treasury for the rising Olympic bill.