Labour will oppose Heathrow expansion because the airport will never meet the party’s environmental tests, the shadow chancellor has said.

Speaking at a fringe event organised by the No 3rd Runway Coalition at last week’s party conference, John McDonnell said the third runway was “never going to happen”.

Officially Labour will support the plan provided Europe’s biggest airport passes tests involving noise, carbon emissions and sharing wealth.

However, Mr McDonnell, whose constituency covers Heathrow, effectively pre-empted the process by saying the tests could not be met, The Times reported.

The two-and-a-half-mile runway aims to boost capacity at the airport by 50%, allowing 740,000 flights a year.

Heathrow insisted the tests would be met.