In the lead up to the Conservative leadership contest, the Northern Ireland Protocol was one of the most prominent and controversial political issues facing Britain.

One of the final two candidates, Liz Truss, is associated closely with the bill that the government hopes will neutralise the Irish Sea border. Indeed, some commentators suggested she took a tough stance on the protocol specifically to improve her chances of becoming leader. Surprisingly, then, this legislation, and the problems that it is designed to solve, have scarcely featured in the debates and policy briefings that have taken place so far.

Is there a reason for this curious omission? Have Liz Truss and Rishi Sunak avoided the topic deliberately, or has the media overlooked an issue that could shape the whole UK’s constitutional future?

One obvious explanation is that the electorate for this internal party battle is composed of Conservative Party members. These activists are frequently assumed to be excited most by low tax, small state economics and Boris Johnson was criticised by the Tory right for neglecting these ‘fundamental’ aspects of modern Conservatism.

As a result, the debate between Truss and Sunak has centred on proposed tax cuts, as well as the candidates’ attitudes to borrowing money and public spending. They are both keen to claim that their economic ideas are in a tradition that included Margaret Thatcher.

Truss was quicker to advocate tax cuts, while Sunak initially argued that unfunded giveaways would increase inflation and worsen the deficit. More recently, though, with his campaign seemingly struggling, he promised to remove VAT on energy bills for a year and, eventually, slash the basic rate of income tax by 4p.

These are serious issues undoubtedly, but so too is the UK’s constitutional future. The protocol cut Northern Ireland off from the rest of Britain economically and politically. It restricted the government’s authority over an integral part of its national territory, divided the UK’s internal market and imposed extra paperwork and costs on British businesses.

Meanwhile, the SNP has made it clear that it will try to force the new Tory leader to hold another referendum on Scotland seceding from the Union and, failing that, nurture a running grievance against Westminster, which it claims is denying Scots a say on their future. A new prime minister, particularly one from the Conservative and Unionist party, will have to put these challenges to the UK’s integrity near the top of his or her agenda, if not at the very top.

Truss has spoken more frequently and forthrightly about the Union, before and during the leadership battle. At a hustings in Exeter, she reiterated her determination to deal with the protocol, even if it meant confronting Brussels. “I think that we’ve learned from history that there is one thing that the EU understands, and that is strength,” she stressed.

Truss has also expressed her disdain for Nicola Sturgeon and Scottish nationalism openly, while Sunak criticised her suggestion that the first minister’s demands for a vote on secession should be “ignored”. That may be a fair criticism, but he co-opted nationalist language and talked about the “four nations” of the UK, rather than emphasising our common Britishness. He is also favoured fairly openly by many figures in the EU, who assume that he will take a less belligerent approach to Brussels than his opponent.

Despite this perception, the Chancellor has claimed that the government’s protocol bill can be used to solve problems with the Irish Sea border and restore the flow of goods from Great Britain to Northern Ireland. There is a difference, though, between supporting the legislation’s passage and actually using its powers, many of which depend upon the discretion of ministers, to set aside checks and paperwork.

This is the type of detail that the debate has not yet touched upon properly so far, even when Northern Ireland and the Union have been the subject of soundbites and vague promises. There is an assumption among many Ulster unionists that Truss would be a louder and more robust advocate of the Union than Sunak, but, so far, it is based on limited evidence.

That may change soon. The Tory candidates are expected to conduct a members’ hustings in Belfast later this month. The audience will include Conservatives and Unionists who feel let down by the government and isolated from the rest of the UK. They are unlikely to be fobbed off easily by unconvincing or incomplete answers.