There is one point on which Ukip, the SNP and the Green Party agree: the problem with Labour and the Conservatives is how alike they are. All three deploy the hackneyed charge that not a “cigarette paper” would pass between them.

At times in British politics this claim has appeared plausible. Around 2006 and 2007, the ideological terrain on which Labour and the Tories fought was microscopically small. For fear of being viewed as anti-business, the former would not propose tax rises on the wealthy. For fear of being viewed as anti-state, the latter would not propose cuts in public spending (agreeing in September 2007 to match Labour’s expenditure levels for three years). The portmanteau “Blameronism” was coined to describe the banal consensus between the two parties, just as “Butskellism” stood for that of the postwar era. It felt as if politics had been reduced to a contest between rival management teams, rather than a clash of ideologies.

It was the crash that brought this era to a close. By ending the illusion of permanent growth, it resurrected the distributional questions rendered irrelevant by the boom. As a result of the shrinking economy, it was no longer possible for Labour and the Conservatives to pledge to avoid both tax rises and spending cuts: choices had to be made.

The two parties have made different ones ever since. In the months that followed the crash, the Tories opposed Labour’s fiscal stimulus and relinquished their commitment to match the government’s spending plans. Gordon Brown broke the decade-long taboo on increasing the top rate of income tax by raising it first to 45 per cent and then to 50 per cent. Politicians retrieved the works of Keynes and Hayek from the shelves where they had long gathered dust.

After 2010, the gap between the two parties grew wider still. Labour elected Ed Miliband as its leader. His defining aim was to overturn the 30-year consensus against market intervention. In office, David Cameron proved more radical than his emollient manner and One Nation rhetoric suggested, unleashing the private sector in areas where Margaret Thatcher had feared to tread.

Most in Westminster agree that the ideological distance between the two parties is now greater than at any time since 1992 and possibly earlier. Labour would restore the 50p rate, introduce a mansion tax, roll back privatisation, maintain Britain’s membership of the EU and impose spending cuts of about £7bn. The Tories would avoid tax increases on the wealthy, extend privatisation, stage a referendum on whether to leave the EU and impose cuts of about £33bn. When Britons go to the polls on 7 May, they will be offered two vastly different conceptions of the country’s future.

The irony is that ever fewer recognise this. The charge that the main parties are “all the same” is levelled with far greater frequency now than in the age of Blameronism. The Greens and Ukip, largely irrelevant until this parliament, flourish as more authentic representatives of left and right respectively. This paradox is partly explained by the degree of policy overlap that remains. None of the main parties has pledged to reject the free movement of people within the EU (as Ukip has), to abandon Trident (as the SNP has), or to end austerity (as the Greens have). Miliband has noted how “the bar” has been continually “raised” as policies once viewed as daringly radical are quickly becoming normalised. Cameron could say much the same in the case of immigration and Europe. His pledge to stage an EU referendum – a first for a Conservative leader – was simply banked by his party’s Brussels-bashers.

If the bar has been raised, some will argue that the answer is to jump higher. It would no longer be surprising if at least one of the candidates in the next Conservative leadership contest advocated withdrawal from the EU, or if a member of Miliband’s shadow cabinet, most likely Andy Burnham, ran to his left in a Labour equivalent.

But even if one assumes this represents an answer, it is a partial one at best. When voters cry, “You’re all the same!” they are rarely referring to policy. Their complaint instead reflects how indistinguishable politicians seem in appearance, manner and accent. It reflects a disdain for the wearying cycle of rebuttal and counter-rebuttal. Politicians may be on different teams but they are still playing the Westminster equivalent of the wall game. Intellectually, Miliband stands outside of the consensus but because of his orthodox career path, he continues to be seen as a creature of the establishment. Neil O’Brien, the former head of Policy Exchange who now serves as an adviser to George Osborne, was told in one focus group that the Labour leader went to Eton.

Voters’ alienation from Westminster derives less from policy than it does from culture. One of the first MPs to recognise this was Jon Cruddas, the head of Labour’s policy review. For this reason, he is perhaps the party’s most redoubtable champion of English devolution and movement politics. Voters will not be assuaged by “retail offers” handed down from on high. Labour must rebuild itself from the bottom up, a point that community-focused MPs such as Lisa Nandy, Stella Creasy and Alison McGovern have brilliantly grasped. The same is no less true in the case of the Conservatives, a party culturally estranged from the blue-collar voters on whom its past majorities depended.

With so few switching between the big two, Labour and the Tories are locked in comparable struggles to squeeze their smaller opponents. But just as the causes of their rise are not short-term, so the solutions will not be either. As one Scottish Labour MP told me in the case of the SNP: “Our biggest opponent is time.” The danger is that an inconclusive election result, produced by a voting system incapable of reflecting individual preferences, will only widen the gulf between Westminster and the rest.