Heathrow Airport expansion: A 'toxic' dilemma for ministers

Heathrow Airport says the proposed runway on the left would bring £211bn in economic benefits

"Toxic" is how one minister described the government's dilemma over Heathrow.

In fact, the whole issue is so fraught that the country's most senior civil servant, Sir Jeremy Heywood, wrote to government ministers in the run up to the politically-charged conference season, warning them against speaking out.

Sir Jeremy's email said they could repeat statements they had made before the report was published in July, but urged them to keep quiet now.

It was received by some with deep irritation.

One cabinet minister told me it was "unprecedented". Other ministers believe the letter illustrates the political sensitivity of the decision.

The Cabinet Office said they would not comment on leaked documents, but the anxieties in government are real and are twofold.

There are concerns over any comments making the final decision more vulnerable to a legal challenge - tying up the decision in the courts for years to come.

And there is significant political opposition around the cabinet table, including from the London Mayor, Boris Johnson.

Decades of dithering

He, along with others, is all too ready to remind David Cameron of his own vow in 2009, "no ifs, no buts", ruling out a third runway at Heathrow.

But the business community is eager for a decision to be made, after decades of political dithering.

And the government, particularly the chancellor, have made big promises about pushing ahead with big infrastructure decisions, even citing the Airports Commission as an example of how the case for major projects should be independently made.

But resistance to Heathrow is passionate and powerful. The prime minister and the chancellor have promised to make a decision by Christmas, but that promise won't be easy to keep.