Speculation is growing that plans for a four-runway Thames Estuary hub airport could finally be sunk this week.

The government-appointed Davies Commission, which is examining options to increase aviation capacity in the south east, is reported to be poised to dismiss the scheme planned for the Isle of Grain.

If so, the announcement would effectively draw a line under the "Boris Island" proposal that has been widely-opposed in Kent and Medway.

Council leaders, MPs, residents and environmental campaign groups have all voiced their opposition to a scheme they believe would be too costly and environmentally damaging to the area.

However, there has been some support from businesses in both Medway and Kent.

Writing in The Telegraph today, Mr Johnson said: "What frustrates me is that a third runway [at Heathrow] is so desperately short-sighted.

"You could not conceivably get it built before 2029, by the airport's own admission – and as soon as it opened it would be full."

Expanding Heathrow would be "barbarically contemptuous of the rights of the population", whose health he said would be put at risk.

The ambitious scheme for an estuary airport suffered a serious setback in July.

Three reports were published suggesting the costs could spiral by billions of pounds, taking into account compensation to the owners of Heathrow, the need for new roads and other infrastructure and removing SS Montgomery, a sunken wreck with explosives.

If Boris Island is rejected, the focus of Howard Davies' investigation will turn to whether Heathrow or Gatwick should have an extra runway.

If it is the latter, the government could face opposition from west Kent, where there are long-standing concerns over noise from flights.