The publication of a draft withdrawal agreement today will confirm once again the central role which Ireland has assumed in the debate about Brexit.
To some extent, this looks likes opportunism. Theresa May's commitment to the DUP, that there will be no border between Northern Ireland and Great Britain, has become a transmission mechanism, making the Irish question a proxy for the future of the UK as a whole.
There is also something deeper at work, however. Attitudes to the European Union and to the Good Friday Agreement are themselves rooted in wider ideas about sovereignty and national identity.
In the case of the strand of conservatism now driving Brexit, I would argue that some perspective on those ideas can be gleaned by looking back at the tradition of High Toryism associated with the name of Lord Salisbury, who became Prime Minister three times at the end of the Nineteenth Century. His premierships were characterised by political quietism underpinned by economic hegemony. A policy of 'masterly inactivity' in Europe that David Davis would be proud of, was combined with a privately driven imperialism still commemorated by the bust of Cecil Rhodes in Liam Fox's office.
Salisbury was closest, however, to the landed interest which then dominated the House of Lords, and as such a natural opponent of Irish Home Rule. His opposition to the Liberals and to the Irish Parliamentary Party on this question, arguably helped to pave the way for the rise of the Labour Party and Sinn Féin, as well as Irish independence.
This High Tory tradition survived into the era of the peace process. As Leader of the Lords in the 1990s, the 7th Marquess of Salisbury, (then Lord Cranborne) was a key pro-unionist voice in John Major's cabinet.
Major's autobiography credits Cranborne with steadying nerves on the Tory backbenches after the leak of the Anglo-Irish Framework Document in early 1995 to Matthew D'Ancona of The Times, a strong critic of Major's approach. This was, conversely, a reflection of Cranborne's closeness to those behind the leak.
This was widely attributed to Friends of the Union, a Tory ginger group set up to oppose the Anglo-Irish Agreement of 1985. The Mail on Sunday reported at the time:
Last night it was becoming clear that a caucus of fervent Loyalists under the umbrella of a Unionist study group is closely associated with the leaker. It is made up of PR man David Burnside, D'Ancona himself; Dean Godson, a Daily Telegraph staff reporter; Paul Goodman, Northern Ireland correspondent on the Sunday Telegraph; Noel Malcolm, a historian and Daily Telegraph political columnist; Andrew McHallam, executive director of the Institute for European Defence and Strategic Studies; Charles Moore, editor of the Sunday Telegraph; Simon Pearce, a Conservative election candidate; company director Justin Shaw and historian Andrew Roberts. One of the group said last night: 'We didn't want the position when the framework document was published of being out in the cold as we were over the Anglo-Irish Agreement in 1985. There was a coming together of minds over what should be done.'
Dean Godson's biography of David Trimble adds more details. The leaked draft was obtained by Burnside, who told Unionist leader James Molyneaux to raise it with Cranborne, as the key unionist supporter in the cabinet, and arranged for it to be passed to D'Ancona.
Major took the view that the leak had 'very deliberately torpedoed' any chance that the Framework Document could get a fair hearing from the unionist public. The weakness of his parliamentary position in the face of such opposition was one reason why the Good Friday Agreement had to wait for a Labour Government.
In the years after 1998, Dean Godson emerged as a key critic of the agreement, helping to inaugurate a neoconservative strand of opposition which I have examined elsewhere. Michael Gove's early anti-agreement pamphlet, The Price of Peace, also belongs to this genre. Gove was also the founding chair of the think-tank Policy Exchange, which is now, under Godson's leadership, the driving force in the campaign for Ireland to follow the UK out of the European Union.
As the Conservatives moved towards power in 2010, High Tory unionism re-emerged. In January that year, the ancestral home of the Earls of Salisbury, Hatfield House, was the venue for talks on unionist unity between Shadow Northern Ireland Secretary Owen Paterson, the DUP and the Ulster Unionists.
The hope was that joint unionist candidates in Northern Ireland would provide a solid bloc to support a minority Conservative Government at Westminster. Had it borne fruit, the strategy would have had a polarising effect on elections in Northern Ireland. As it was, it sat uneasily within any notion of bipartisan support for the peace process. The prospect of a Conservative government cannot have discouraged the DUP from taking a hard line in the talks over the devolution of justice, which collapsed in the same month as the Hatfield House talks.
In the event, the reckoning was postponed by the emergence of a Conservative-led government dependent not on unionists, but on Liberal Democrats. It was nevertheless notable that the coalition treated the Northern Ireland Office as a Conservative fiefdom, matching the Lib Dem dominated Scotland Office.
With the slim Tory majority of 2015, the Orange card came back into play. With the minority government of 2017, it became decisive. In between, the Brexit referendum gave the initiative to the Tory right.
Even before Brexit, High Tory unionism represented a threat to the Good Friday Agreement. That is now only one dimension of an alliance that risks turning the clock back to Salisbury's Britain, an era of rentier torpor at home and adventure capitalism abroad.