MORE doubt has been cast on the prospect of the so-called “Boris Island” Thames Estuary airport plan going ahead.

Four official reports have poured cold water on plans for a four-runway airport opposite Southend on the Isle of Grain, favoured by London mayor Boris Johnson.

One of the three reports prepared for the Airports Commission, which is considering how to expand airport capacity in south east England, said: “The challenges are considerable and amount to a significant cost and risk to the taxpayer.”

Another said Heathrow's owners would have to be paid compensation of between £13.5 billion and £21.5 billion as the UK’s airport would have to close.

A third cited possible transport improvement costs associated with the new airport of between £10.1 billion and £17.2 billion.

Southend Council leader Ron Woodley said: “Everyone realises there are substantial obstacles to the scheme.

“We are opposed to the estuary airport because we don’t see any benefit to the town.”