A pro-Heathrow expansion group has hit out at Boris Johnson 's 'hypocritical' move to invest millions into Heathrow Airport , even though he publicly opposes a third runway .

A Greater London Authority (GLA) internal audit report revealed that £3.5 million of public money has purchased a bond in 'Heathrow Funding Ltd' (HFL).

HFL is a company with the primary purpose of raising funding from external sources to provide money to Heathrow Ltd subsidiaries – with proceeds distributed to Heathrow Airport Ltd.

The proposed third runway expansion is expected to cost a total of £16 billion including the 3,500 metre North-West runway, infrastructure, terminal, “community compensation” and buying land and property.

Rob Gray, Back Heathrow’s Campaign Director, says the “hypocrisy and double-standards” of the mayor is “truly astounding”.

He told getwestlondon : “London taxpayers will be dumbfounded that a man who has actively campaigned against Heathrow would be hypocritical enough to allow the GLA to purchase a £3.5m corporate bond in the airport, despite his vocal opposition to its very existence.

Mr Gray reiterated the existing “massive support” for Heathrow expansion , “from the majority of UK businesses, international airlines, local firms and most importantly, from local residents".

He said: “They all want to ensure Heathrow grows in the future so that existing jobs are secured, and future jobs are created.

“If the member for Uxbridge and South Ruislip would like to join them, he need only say.”

Christine Taylor, of Stop Heathrow Expansion, would like a response from the mayor about why this decision was made.

She said: “We don't believe it's his decision but we feel we need an answer as to what is happening with Londoner's money.

“I can't believe he would approve that sort of investment – it's illogical to be fighting Heathrow expansion and then funding it through the back door.

“I'd be curious to know how much in total has been invested in Heathrow and over what period. I would that the mayor would reveal this and give his reasons why.”

'A pathetic excuse'

A GLA spokesperson has not denied the investment into Heathrow Funding Ltd.

They said: “The GLA has a duty to ensure its short-term cash balances are invested with an aim of minimising the risks of any loss to the taxpayer.

“Those investments are made by officials in the Group Treasury Team, without political involvement and targeting high quality and creditworthy institutions.

“The Mayor's opposition to a third runway being built at Heathrow airport is extremely well known however the airport remains a business of the type that is suitable for this type of investment.”

Harmondsworth resident, Ms Taylor, thinks the GLA's reasoning is a “pathetic excuse”.

She said: “Nobody can be in any doubt that London is polluted and the source of that pollution to a large extent, in our area, is the airport.

“I think it's irresponsible of financial teams not to bear that in mind when looking at investments.

“Whatever investment judgements they make they have to bear in mind the implications. We would hope they would look at more ethical investments and not invest in a pollutive industry.”