Planes, promises and airport taxes
When is a promise not a promise?
This vaguely philosophical question recurs during many of the parliamentary debates on Brexit.
The UK government's answer, as voiced by Wales Office Minister Guto Bebb is this: "To claim that promises made in a referendum campaign are binding on government is in effect a nonsense."
The promises in question concern the future of funding that currently comes from the EU for the poorest parts of Wales. Aberavon Labour MP Stephen Kinnock told a Westminster Hall debate on Tuesday: "While the leave campaign made promises that all EU funding would continue to flow to Wales at the same levels, I think we know that those promises are about as valid as what could be printed on the side of a bus."
Torfaen Labour MP Nick Thomas-Symonds wasn't the only "remainer" to begin his remarks by acknowledging the referendum result before adding a "but".
He said: "I totally respect the result of the referendum of 23 June, but it does not mean that the leave campaign can escape from the promises that were made in the weeks and months leading up to it. What promises were made? I have with me the letter written on 14 June, released under the headline, "Leave Ministers commit to maintain EU funding".
"What did they say exactly? The letter states: 'After protecting those now in receipt of EU funding, we will still have billions more to spend on our priorities. We propose that at least £5.5bn of that be spent on the NHS by 2020, giving it a much-needed £100m per week cash transfusion, and to use £1.7bn to abolish VAT on household energy bills'."
Some of the ministers involved are now in the government. Mr Bebb told Mr Thomas-Symonds the letter of June was trumped by a Treasury guarantee of October - and that the issues he raised implied a lack of understanding of how a referendum campaign works. "It is not about electing a government," he said.
"In the referendum campaign there were members of the Labour party on either side of the argument, and the same was true of the government. To claim that promises made in the referendum campaign are binding on government is in effect a nonsense, and I think that you know it".
So that promise is presumably as irrelevant now as George Osborne's promise of a "punishment Budget" if Britain voted to leave. And all promises made by ministers in the "remain" camp seem to have been trumped by the public vote for Brexit. Hence we now have a pro-remain prime minister having to deliver a policy she voted against.
Theresa May is also trying to deliver an airports policy she thought would "devastate" her constituents.
The decision to expand Heathrow (despite David Cameron's promise not to go ahead) has been welcomed by Welsh Secretary Alun Cairns who said he was pushing for that option in cabinet (although, unlike the Scottish secretary, he was not given a seat on the airports cabinet sub-committee).
Mr Cairns has also defended the UK government's refusal to give the Welsh government control of air passenger duty. The Vale of Glamorgan MP, whose constituency includes Cardiff airport, said: "We've looked closely at this and because South Wales uses both Bristol airport and Cardiff airport we've assessed there would be a potential net loss in the flights that leave both airports."
He added: "People who are calling for the devolution of air passenger duty are assuming that the Welsh Government would cut it. Now our experience is that every tax that they control up until now has led to an increase so we're determined to protect the passengers that use Cardiff airport."
In Welsh politics, the default response to large infrastructure projects in England is, understandably, to see if Wales can get a cut of the cash.
Mr Cairns said Wales would get its "fair share" of extra public spending on infrastructure work linked to the expansion of Heathrow but stressed that the project would be "almost entirely privately-financed" so the Welsh Government shouldn't draw up its wish list just yet.