This week has already seen a considerable deal of heat over Theresa May’s “grubby,” “shameless,” “reckless,” “sensible,” “value for money” – take your pick – deal with Northern Ireland’s Democratic Unionists.

It is interesting to note it covers just two years. No doubt, the largesse the DUP has received will be repeated in 2019 to maintain the 10-MP lifeline Arlene Foster’s party has thrown her fellow Unionists, which will take us beyond Brexit and, possibly, beyond the tenure of the current Prime Minister.

The SNP and Labour have been in high dudgeon over the £2.9 billion, they say, should be coming Scotland’s way under that dusty, old mechanism known as the Barnett Formula.

To press the political point home, an outraged Derek Mackay, the Scottish Government’s finance secretary, has written to Liz Truss, the chief secretary to the Treasury, threatening to invoke an official disputes procedure. Scotland, he told MSPs, had been robbed.

Labour calculated that, based on population share, Wales should get £4bn and England a whopping £59bn on the back of the deal for Northern Ireland.

But the Treasury has insisted the DUP deal is, like the raft of city deals, outwith the Barnett Formula, which, as funding expert, Professor Professor Gerald Holtham of Cardiff Metropolitan University, has stressed worked “in one direction only”; that is, the Government produces extra spending for England and then the devolved nations get their proportionate share. It did not, insisted the good professor, operate in reverse.

But such arguments have not stopped the political attacks. The SNP at Westminster felt they had David Mundell on the ropes after he declared last week: “Any funding that goes to Northern Ireland, then Barnett rules will ensure the appropriate funding comes to Scotland."

Ian Blackford, the SNP leader, suggested the Scottish secretary’s position was untenable given the Government’s official position. Mr Mundell swiftly appeared on the telly to insist everything was transparent and there had been “no subversion” of the Barnett rules.

He also noted how it was only a year ago the SNP was arguing for Scotland to be outside the Formula and have full fiscal autonomy, which, he claimed, “would’ve cost Scotland billions”.

Not letting up, the SNP’s champion Pete Wishart urged John Bercow to allow for an urgent Commons debate ahead of Thursday’s vote on the Queen’s Speech so MPs could examine the Con-DUP deal.

Suspecting, perhaps, a point-scoring-fest, the Speaker respectfully declined. We'll get that today at PMQs.