Plans for an airport in the Thames Estuary have been branded "absolutely nuts" by the boss of a commercial airline.

The floating airport, nicknamed Boris Island after London mayor Boris Johnson who has championed the plans, would not make economic sense according to Michael O'Leary, head of Ryanair.

The proposal is to build four-runways off the coast of Medway which would replace Heathrow.

Mr O'Leary, chief executive of Ryanair, believes there is no need for a new airport, and existing ones should be expanded instead.

He told the BBC said: "I think it's absolutely nuts, there's no requirement for any new hub airport.

"London has five airports - you've got Luton, Heathrow, Gatwick, Stansted and London City - what you do need and we need urgently in the South East is more runways at those airports."

Mr O'Leary said the airport, which he called a white elephant, would be a waste of money and its location would mean billions of pounds would need to be spent linking it to London.

He added: "It would cost billions, it would take probably 20 or 30 years to develop and open, and then it would cost even more billions to connect it to central London.

"Please, please don't waste billions and billions of pounds of tax payers money building palaces for Boris Johnson in the marshes or the Thames Estuary.

"It doesn't make sense and it's the wrong way to develop Britain's airport infrastructure in the South East."

Boris Johnson has backed a report, overseen by Transport for London, which called for a new hub airport to meet passenger demand but the plans have gained little support elsewhere. Medway Council, Kent County Council and wildlife groups have all rejected the idea.

Prime Minister David Cameron said the government had no plans for a estuary airport, after the issue was raised by Gillingham and Rainham MP Rehman Chishti in the House of Commons in October last year.

The plan has also been criticised by the Board of Airline Representatives and the boss of Virgin airlines has opposed the scheme, saying it was the wrong side of London.