A proposed super airport in the Thames Estuary would require £30bn in public subsidy and would not be commercially viable, an unpublished parliamentary report will say.

The report, by transport consultancy Oxera for the Transport Select Committee, shows that the expected revenues generated by the airport – dubbed Boris Island on account of London mayor Boris Johnson’s support for its construction – would be insufficient to justify building it, without a massive contribution from taxpayers.

The public subsidy required for a four runway hub would be around £30bn, the report will say – even if London Heathrow is closed to reduce competition for passengers and the taxpayer funds the surface transport to the airport separately.

“That is an optimistic view,” a source told Professional Manager. “Because there is nothing to stop Gatwick building a new [competing] runway. This [report] assumes no other runways are being built.”

Although researchers working for Oxera looked at a variety of different scenarios, all would require hefty input from the taxpayer to make them viable, the source revealed. Asked whether the proposed facility would be commercially viable, the source said: “The answer is, unequivocally, ‘No.”