How do you campaign against a party like Ukip? This is the question occupying Labour and Conservative strategists as they prepare for the 2015 general election. One place they could start is by recognising the scale of political inequality in modern Britain and that a large number of voters feel utterly disconnected from our political process.

The depressing scale of political inequality was brilliantly captured by the Electoral Reform Society, which looked at how our main parties spent money at the last general election. It found huge geographical differences. If you lived in the most valuable seat in the country (Luton South) it is good news; £130,000 was ploughed into contacting voters, including almost £3,000 on public meetings. This meant a vote was effectively worth £3. But if you lived in the least valuable seat – the ultra-safe Labour seat of Bootle – it is a different picture; barely £5,000 was spent, no money was devoted to public meetings and a vote is worth less than 20p. This is not exactly what John Stuart Mill had in mind when he talked of an equal democracy representing every citizen in a proportionate manner.

It’s not the fault of the parties (although their failure to offer serious alternatives to first-past-the-post speaks volumes). It is the fault of the system, which only prospered when Labour and the Conservatives could attract more than 80% of the vote and there was no appetite for challengers. But that era is gone. In other systems, parties have incentives to engage with more voters. But in Britain – where only one in three of us live in a marginal seat – such incentives do not exist. Instead, we are left with a democracy where parties spent 162% more money in the 50 most competitive seats than in the 50 least competitive. Chances are, you are one of the 20 million who live in a safe seat and so won’t be hearing much from our parties next year.

Is it any wonder that voters are turning to parties like Ukip? When some voters are valued 22 times more than others simply based on where they live, you have space for populists. This political inequality validates their claim that politicians “are not listening”. It is why last month Ukip announced that it wants to rebuild trust in politics and give voters a greater say through Swiss-style referendums. It is also why Nigel Farage ordered his activists at the last elections to hold as many public meetings as possible. Perhaps he had read the research; in almost one in three seats at the last election, almost no money was spent by the main parties on public meetings. My own calculations suggest the picture is bleaker; in more than half of all seats not even £100 was spent on public meetings.

As our grassroots democracy has hollowed, Farage has toured the country, speaking to voters and (as he told me) “hanging around for a couple of hours afterwards to hear whatever was on their minds”. Compare this with the stage-managed events of our main parties – a few workers huddled in a factory, glazed expressions, listening to an overly wonkish policy announcement.

The main parties often ridicule Ukip for not having a voter identification system that can match their short-term electoral professionalism. But they miss the point; over the long haul, the strength of populist parties flows from their repudiation of these bland techniques. You will not resolve voters’ grievances by treating them like a focus group.

The implications of all this are reflected in other evidence. I’ve looked at the 20 seats that saw the lowest amount of spending. They include places such as Ashton-under-Lyne, Doncaster Central, Halton, Knowsley, North Tyneside, Rotherham and Sheffield, where parties spent a paltry 34p per vote. Fast forward to the European parliament elections this year. In all these places Ukip finished second, with at least 20% of the vote. Bottom of the list was Bootle, where Ukip averaged 28% – just six points behind Labour.

Labour and Tory strategists will respond with something like: “Yes, but Ukip will not win parliamentary seats.” This is what is wrong with our representative democracy – it ignores a groundswell of public discontent with how the system is working. Elections are supposed to offer us all an equal chance to join a national conversation about our society and how it can be improved. But our system is encouraging the main parties to ignore a large swathe of voters and is chipping away at our basic right to participate meaningfully in politics, thus creating fertile soil for populists.