How long will DUP prop up May and Tories?

The Tories' pact with the DUP looks very much like a deal to prop up this minority government for the two years which in theory are necessary to deliver Brexit.

Because of the £1bn government sweetener promised to Northern Ireland, the big money for investment in health and infrastructure there is all deliverable over two years.

And although the so-called "confidence and supply" arrangement is for the lifetime of the Parliament, its details are renewed at the time of every Queen's Speech legislative programme - and the current one lasts (as you will recall) also a Brexitly (sic) synchronous two years.

What's more the DUP is promising not just to support the government on the Queen's Speech, Budget and those "confidence" votes that could bring it down, but also on all Brexit-related legislation.

Theresa May watched on as chief whip Gavin Williamson put his name to the historic paperwork. Credit: PA

So for two years at least the government should be a bit more stable, if not exactly strong, as a result of the alliance with the DUP.

But that does not mean T May will survive as Tory leader or PM for that period, or that the DUP would hope and expect her to do so.

Because what is very striking is that she has not signed the agreement with the DUP. It's been signed by her chief whip Gavin Williamson.

Which implies that the pact could survive her resignation or eviction.

Both party leaders face pressure after doing the deal to restore the Conservatives' majority in the Commons. Credit: PA

Or to put it another way, the DUP does nothing to undermine the widespread notion among Tory MPs that she could quit in about a year, or possibly even this autumn, and that there would be a General Election in the spring/summer/autumn of 2019, following the UK's formal departure from the EU.

That highly plausible timetable for attempted Tory renewal and the next election is completely consistent with the DUP deal.

PS. All the above is predicated on Dublin and Sinn Fein being persuaded that the DUP pact does not breach the spirit of the Good Friday Agreement, namely that the UK government remains an impartial guarantor of that agreement.

If their trust in the good faith of Theresa May were to be seriously impaired, the consequential mess would be yet another crisis for her - and one she would probably not survive.

The DUP deal package could possibly be as much as the rumoured £2bn they were demanding. Credit: PA

PPS. DUP sources tell me I have undervalued the wonga they have prised from the Treasury.

They say that a relaxation of constraints on access to an existing £500m pot for education investment, under the 2014 Stormont House Agreement, should be factored in by me.

And also that the promise that NI will get some additional Enterprise Zones will be highly valuable.

So in total the package of support they've won is certainly more than £1.5bn - and possibly as much as the rumoured £2bn they were demanding.

Damian Green, left, has confirmed the pact signed by Gavin Williamson, right, stands even if Theresa May stood down as PM. Credit: PA

And, by the way, they will have the ability to shape and influence the government's policy-making and direction via membership of a "coordination" committee, which will me chaired by a minister (probably the Chief Whip Gavin Williamson or the First Minister Damian Green).

Which will worry liberal Tories who dislike the DUP's opposition to gay marriage, inter alia, and fiscally conservative Tories, who mistrust the DUP's opposition to austerity.

"Dogs", "tails" and "wagging" all come to mind.

PPPS (If there is such a thing!) Damian Green has confirmed to me that the DUP pact would continue, even if Theresa May stood down as PM - because it is an agreement between the parties, signed by the two chief whips, and not between the parties' leaders.