The current general election will already be quite enough for most readers. Not even a masochist in an anorak will yet have given any serious thought to the one that comes after it. As things stand, that general election is now due on 5 May 2022. But not if Theresa May has her way.

The Conservative general election manifesto contains a single sentence which has received little attention. “We will repeal,” it says, “the Fixed-term Parliaments Act.” On the face of it, this is a clear pledge. But the manifesto is silent about what Mrs May intends to put in its place. And that’s where the trouble starts.

The Fixed-term Parliaments Act was passed by the Conservative-Liberal Democrat coalition in 2011. It confirmed that general elections should take place on a fixed day every five years. It removed the traditional royal prerogative power, exercised by the prime minister, to trigger an early election. It said that two-thirds of MPs had to approve a motion for an early one to be called. This was regarded as a significant contribution to the stability of government. Yet in April Mrs May moved such a motion and it was carried.

Repealing the 2011 act would not be as simple as it may seem. Lawyers disagree as to whether a royal prerogative that has been ended can be brought back to life by repealing the act that ended it. It seems likely that, if Mrs May wins the 2017 election, she will have to introduce new legislation expressly giving parliament the power to set a maximum term and the circumstances in which an early election can be held. There is some anxiety about allowing politicians to tinker with a core aspect of the constitution, all the more acute after the drubbing the prime minister’s reputation for political probity has suffered in the past month.

So, if Mrs May is at all sensitive about the issue, her new bill will need to take care inventing a procedure. To confer a prerogative power on a prime minister might strike some as legitimising a form of autocracy strongly at odds with the parliamentary system. Yet to confer the power on parliament – which would ensure that the prime minister could only stay in power with the confidence of the house – also means that the existing system, which Mrs May seeks to repeal, would effectively continue.

Mrs May could lower the two-thirds threshold. She might decide that a simple majority of MPs was sufficient to dissolve parliament. That would hand a lot of power to her backbenchers, especially in a parliament with a small majority. If Mrs May wanted an early election to confirm the outcome of the Brexit talks, for instance – and if she is not contemplating that possibility, it is hard to see why the repeal of the Fixed-term Parliaments Act is in the manifesto – some of her MPs might be able to stop her. The result might be a zombie government, which the opposition parties were content to leave on the rack.

There are other options. Mrs May could use the bill to prohibit a snap election too close to the previous contest, or too close to the scheduled one. She could insert a clause similar to those that apply in the Scottish, Welsh and Northern Ireland devolved elections, in which a snap poll only allows the victorious government to serve out the rump of the previously scheduled parliament. Or she could change the five-year fixed term to four years. In the end, politics will out, just as happened in April under the existing act.

But it isn’t obvious why the repeal of the 2011 act is in the Tory manifesto. Mrs May, after all, has managed to engineer a snap poll this time, so the act has not got in her way. Together with proposals ending proportional representation for some local elections, it looks as if she wants to reverse efforts to modernise democracy. Mrs May should reconsider: after the reputational damage she has sustained in this election campaign, she would be foolish to make changes that might suggest that her appetite for power was more important than respect for democracy.