One of the most persuasive themes of modern political history is the decline not just of the two-party system but the three-party system as well.

It is no longer possible to talk about our “three main political parties” without qualification. Do you mean the three main parties in England? Because they are different to the three main parties in Scotland, Wales and Northern Ireland. And do you then mean the three main parties in south-west England (Con, Lib Dem, Ukip)? Or north-east England (Labour, Ukip, Lib Dem)? Or maybe London (Labour, Con, Lib Dem)? And so on.

The response during the past 24 hours to the broadcasters’ proposals for national election debates has illustrated this conundrum sharply. Objections have poured in from every corner of the country and every shade of the political spectrum.

But nobody has so far disagreed with the actual premise of holding a debate. And that ought to be the starting point for discussion. The idea of staging “national” debates presupposes there is a national electorate that is homogenous and self-aware. I’m not sure there is. Ditch that assumption and compromise ought to be possible – perhaps agreed in tandem with plans for further devolution to each of the UK nations.

One thing is unarguable, however, and that there will be more time for debates in the 2015 campaign than in 2010. Parliament will be dissolved on 30 March and polling day is 7 May, making the official campaign a whopping 37 days long.

Compare that with just 23 days in 2010, when the debates took place at weekly intervals. This time there is enough space for the debates to take place fortnightly – and this is exactly what the broadcasters have suggested, specifically 2, 16 and 30 April.

This rather undermines David Cameron’s preference for having the debates before the campaign to avoid them “overshadowing” the run-up to polling day. Fortnightly debates would establish a very different rhythm to the campaign than the one in 2010. We would have much longer gaps between the build up and post-mortem for each encounter. Given there’s such a long haul from dissolution to election day, fortnightly debates might even help create momentum where it otherwise might be flagging.

As for the popularity of debates with voters, here’s a reminder of how things unfolded in 2010.

The first debate took place on 15 April. It was broadcast on ITV and watched by 9.4m people: a 37% share of the total TV audience during its 90 minutes on air. It was the most-watched programme of the day, beating both Coronation Street and EastEnders.

The second debate a week later was watched by 4.1m. The drop in ratings was due to it being on Sky News, although it was simulcast on the BBC News channel and Sky3. It was repeated on BBC2 later that evening. 2.1m people watched it on Sky, 1.4m on BBC News, 0.6m on Sky3 and 0.3 on BBC2.

The third and final debate on 29 April drew an audience of 8.4m. It was broadcast on BBC1 and attracted a 32% share. It was also simulcast on Sky News. The BBC debate was up against stiffer competition than the one hosted by ITV, in the shape of Coronation Street on ITV and a Europa League football match involving Liverpool on Channel Five.

The debates were agreed on 21 December 2009. It then took a further two months to agree the 76 rules under which they would take place. If Cameron wants the 2015 debates to happen before the campaign even begins, he and his team better get a move on.