In July I was coincidentally in Northern Ireland at the same time as the prime minister. I thought we might meet, as we were both invited to speak at Queen’s University Belfast, where I discussed Brexit and the danger of a new Irish border with an audience of unionists and nationalists.

But Theresa May declined the invitation, I assume on the advice of Arlene Foster, who supervised her visit and arranged instead for her to speak to a hand-picked audience.

Her Belfast speech was terrible. If it had been written by the DUP leader – maybe it was – it could not have been worse. It declared the Conservative party, and her government, to be partisans for Northern Ireland as British, 25 years after John Major made the path-breaking declaration, which opened the way to peace, that Britain had no “selfish interest” in Northern Ireland and would act as honest broker between the two communities.

May also disowned the “Irish backstop” that she herself had agreed with the EU last December. The backstop provides, in effect, for Northern Ireland to stay in the EU customs unions and single market in the event of Great Britain leaving them at the end of the Brexit implementation period in 2020, as the only viable way to prevent a new border in Ireland.

Without this backstop the EU would, rightly, have declined to enter into negotiations with May on a post-Brexit economic deal, since the UK would be in breach of the 1998 Good Friday agreement, an international treaty the UK is bound to maintain.

May struggled to avoid the backstop, and was ferociously attacked by Foster and the DUP for agreeing to it. But she and Boris Johnson had no choice – just as, despite the latest bluster, whichever of them is by then prime minister will have no choice but to maintain it in any exit treaty with the EU.

However, there was a poison pill in May’s capitulation to Foster, which she saved up until the eve of the Tory party conference – the proposed Festival of Great Britain and Northern Ireland announced at the weekend for 2022.

There was instant derision. “Parade of empty supermarket shelves”, “flypast of passenger jets unable to leave the country” and “world’s longest lorry queue” were a few of the suggestions.

However, few have woken up to why May announced it as the “Festival of Great Britain and Northern Ireland” and why the timing is significant – 2022 marks a century since the creation of Northern Ireland. You can make a case for 2021 as the official centenary, but 1922 was when the full constitutional revolution in Ireland took place, which saw the Irish Free State break away from the UK with virtual independence after a terrible civil war, while the six most “Protestant” counties of Ulster remained within the UK under a devolved government and parliament sitting in Stormont in Belfast.

The history of Northern Ireland is a battleground almost as bloody as the events it disputes. Lloyd George, who did the ultimate partition deal in a coalition with the Tories, defended it as the best of a very bad job dating back to the rejection by the Conservative party of Gladstone’s 1886 bill that would have given home rule to Ireland as a whole. That was followed by a revolt against any future home rule settlement by Ulster’s Orange movement, cynically and treacherously manipulated by Tory leaders from Lord Salisbury to Bonar Law.

‘The history of Northern Ireland is a battleground almost as bloody as the events it disputes.’ Photograph: Charles McQuillan/Getty Images

Key facts cannot be disputed. Partition in 1922 gave Ireland a hard border, and created a one-party unionist state in Northern Ireland that discriminated against Catholics and deep antipathy between Éamon De Valera’s Ireland and both Britain and Northern Ireland. This led ultimately to the civil rights protests of the 1960s and a collapse into violence and terrorism, which ended in the late 1990s only after a nightmarish 30 years of quasi-civil war and appalling bloodshed thanks to enlightened statecraft by Major, Tony Blair and governments in Dublin.

I suspect May isn’t familiar with the sweep of Irish history. She has devoted less attention to Ireland than any modern prime minister. She hasn’t even done what I and others regard as her bounden duty – to camp out in Belfast until a power-sharing government was formed after the last Northern Ireland election. Instead, there has been no government or assembly in Belfast for nearly two years, and civil liberties and unrest are once again in an alarming state.

But one thing May could do to help would be to cancel her “festival of partition”.

If she is in any doubt, she should read the speeches of Edward Carson, who led the weaponised revolt in Ulster against the elected Liberal government to stop home rule before the first world war. “Now men, remember your arms, and keep them no matter what happens. I rely on every man to fight for his arms and let no man take them from him,” he raved at a military parade of his Orange “army” in 1914 – words taken equally literally by the IRA in fighting Carson’s successors in our own generation.

Never again.

• Andrew Adonis is a Labour peer and former minister