What are the chances that Boris Johnson or Dominic Cummings ever heard of Lundy?

It is unlikely they are aware of how every year without fail an effigy of Robert Lundy is set alight on the top of a huge bonfire in Derry and at many other venues in Northern Ireland.

Lundy is torched because in loyalist culture, he is depicted as the treacherous Governor of Londonderry who was willing to betray the citizens and open the City Gates to the advancing troops of the Catholic King James in 1688.

This afternoon in the Westminster Parliament, while the wider world tuned in once more to the "Order, Order" disorder show, the DUP gave Boris Johnson the Lundy treatment.

For decades during fall-outs with political rivals, the most pointed label used by the DUP in anger was "you are a Lundy."

The late Reverend Ian Paisley used the term about the unionist prime minister, Terence O'Neill, one of his successors as UUP leader, David Trimble, and about the British prime minister, Margaret Thatcher.

Boris Johnson was delivered a body blow by the DUP

Boris "Lundy" Johnson got his comeuppance shortly before 3pm today when the Westminster parliament tellers returned with the result of the Sir Oliver Letwin amendment vote.

It’s a significant level of political heft for a political grouping with 10 MPs to undermine one prime minister.

But the DUP have now stretched to a degree of notoriety and effectiveness unprecedented in the modern history of Westminster.

Today they ambushed Boris Johnson, the Conservative party leader they had helped to oust Theresa May.

The body blow to the prime minister is directly related to his falling out with the DUP earlier in the week.

A DUP delegation almost had front door keys to Downing Street as it sought to influence the Brexit deal that Mr Johnson’s officials were negotiating with the EU.

But when he headed off to Brussels on Thursday morning and abruptly cut off his contacts with the DUP, his Northern Ireland allies were not pleased.

Leo Varadkar (2nd left) after the EU and UK agreed a Brexit deal

They watched the television pictures of a smiling Boris surrounded by EU leaders. They noted the presence of Taoiseach Leo Varadkar, flanked by the EU big boys, Jean-Claude Juncker, Donald Tusk and Michel Barnier. They came home to headlines of "Tory treachery leaves DUP looking foolish" and "DUP proves expendable for Tory old boys’ club."

They heard political rivals saying "I have no sympathy for them as they cry into their cornflakes" and "after years of being wined and dined by their Tory friends, Boris has thrown them under the bus."

They were hurt. Angry. Humiliated. But then, utterly in keeping with the pattern of this Brexit drama, when a predictable storyline seemed to be developing, from left field one more extraordinary and unexpected factor came over the hill.

Oliver Letwin pictured after MPs voted to delay the approval of a Brexit deal

Oliver Letwin was a government minister under Theresa May and her predecessor, David Cameron. He is one of the Tory MPs who voted against Boris Johnson’s Brexit strategy. All lost the party whip so he now sits as an Independent MP.

Letwin’s motion, only tabled yesterday evening, effectively blocked Boris Johnson’s plan to put his Brexit deal to a vote in the Westminster parliament this afternoon. 

Crucially for the DUP, while they were still in "red mist" mode, it gave them the opening to return serve with interest to Boris Johnson after their slighting two days before.

There are rumours that as Boris Johnson departed for Brussels to cut his deal on Thursday, some colourful and unprintable language was expressed by Dominic Cummings over the failure of the DUP to bid his boss "God Speed".

If they had the courage to stay around, the flies on the wall close to Mr Cummings as he reacted to the result of the Westminster vote would have a good story to tell.

The numbers tell the decisive role of the DUP. Oliver Letwin won, Boris Johnson lost by 322 votes to 306. The 10 DUP members were on the winning side. (Interestingly the Independent unionist, Sylvia Hermon, a Remainer, was too). But had Nigel Dodds and his nine DUP colleagues voted the other way, Boris Johnson would have romped home by a four vote margin 316 to 312.

So what happens next? Revenge may well be sweet for the DUP but the party is now in an even more awkward place.

Even some members of the European Research Group, the most hardline Brexiteers in the Tory camp, may be tempted to give them a wide berth, now that they have shafted Boris.

Their likely first step may be to try seeking amendments to the deal brought back by the prime minister from Brussels.

Nigel Dodds in the House of Commons today

They may face a brick wall on an issue that is important to some of the 10, particularly Sammy Wilson and Nigel Dodds. They are irked that a Simple Majority basis would be used in the Consent Function a Stormont Assembly would exercise over the Northern Ireland specific regulatory alignment and customs union proposals. As Sammy Wilson stated during the Westminster debate, the DUP wants the cross community mechanism of the Good Friday Agreement used.

Forty people designate as unionists in the currently mothballed Assembly. That’s 40 out of 90. Using Sammy’s logic, a majority of the 40, that’s 21 or more, would have a veto over the views of the 90. An interesting use of democratic principles.

The put-down delivered by Boris Johnson to Sammy in the Westminster chamber was decisive. The prime minister stated at the dispatch box that the Brexit Referendum was run on a simple majority basis. The same system will apply to the arrangements that flow from it.

After they upended Boris, the DUP members headed for their connecting flights to Belfast City or Aldergrove Airports.

They might have noted the contribution made by Theresa May during the Westminster debate. She looked healthier and many times more relaxed than when she was the one on centre stage.

Boris, her replacement, is the wounded one this evening. 

Nigel Farage and the Remainers must be thankful for the decisive intervention of the DUP.

Boris, the scholar, would be familiar with the phrase "Et tu, Brute." As Nigel Dodds is the leader of the DUP in Westminster, should it be "Et tu, Nigel?"