Boris Johnson has reached for the word compromise many times in the last two days as he has promoted his new Brexit proposals. There were three mentions of compromise in his party conference speech in Manchester on Wednesday, a further four in his letter to the European commission, two in the statement he delivered to MPs at Westminster on Thursday and several others in the exchanges that followed.

These usages, although tendentious, are not wholly specious. Mr Johnson’s proposals are an attempt to bridge the gap between the EU-UK withdrawal agreement signed by Theresa May last year and the root-and-branch rejection of that agreement by the Conservative party’s most dogmatic pro-Brexit faction. Setting aside the fact that Mr Johnson himself voted for that agreement in March, the prime minister has moved the dial a few notches from his previous determination to get rid of the Northern Ireland backstop in its entirety.

However, the new proposals are not a compromise with the European Union, which is the body with which he ought to be seeking a deal. They are a compromise with the Democratic Unionist party. Mr Johnson has courted the DUP more assiduously than even Mrs May did. He has spoken at their conferences, invited them into Downing Street and generally gone the extra mile to find ways of appeasing their demands that Northern Ireland should not be treated differently from the rest of the UK. The compromise Mr Johnson has now made with the DUP allows him to say that there can be some all-Ireland regulations for a limited period – which would mean Britain and Northern Ireland leaving on different terms – while the DUP has secured an effective veto over their further continuation, thus ensuring that Northern Ireland will be fully part of the UK customs territory in the longer term. But they are talking to themselves, not to the wider polities of Ireland, Britain or Europe.

Mr Johnson ignores three huge issues. The first is that the DUP does not speak for Northern Ireland, whose people voted to remain in the EU in 2016 and where opinion polls regularly show support for the backstop and for separate treatment for Northern Ireland to preserve the all-Ireland economy. By allowing the DUP to act as if it is the government of Northern Ireland, Mr Johnson ignores the majority that oppose the DUP’s pro-Brexit stance and mounting evidence that the DUP is now losing the hegemony that it used to enjoy. Giving a decisive role to Northern Ireland institutions that are suspended for intractable reasons solves nothing (and triggers the demand from Scotland that their devolved institutions should get a veto too). It suggests Mr Johnson might not be able to make his deal stick, even if the EU agreed to it.

The second problem is that Mr Johnson’s plans renege on the principles, and legally rooted treaty guarantees, of north-south cooperation that have been the bedrock of the increasingly precarious Northern Ireland peace process. Preserving the Belfast/Good Friday agreement was at the core of Mrs May’s approach. It is part of the EU (Withdrawal) Act itself that the UK will not create any form of “physical infrastructure” for border arrangements after Brexit. The reason why there is a backstop at all is because the May government took these promises seriously. Like so many English Tories in the past and today, Mr Johnson simply does not share that sense of responsibility. His plans betray Britain’s solemn promise and ignore the consequences for Ireland.

The final problem is that the vagueness of Mr Johnson’s plans leaves a hole in the EU single market without proposing a workable solution. Controls of any kind are inconsistent with the principle of frictionless trade, while loose controls threaten rules and protections for consumers. It is typical of Mr Johnson and the hardliners that they have failed to engage with these realities at all.

Yet the realities are immutable. Britain has profound legal and political obligations to the people of Ireland. Britain has deep moral obligations too. None of these are upheld in the government’s new proposals or by the untrustworthy way Britain behaves on the Irish and European stage. Mr Johnson calls it compromise. It should be called perfidy.