Do you listen to classical music, live in the country and socialise with a broad range of people? Or do you live in a traditional manufacturing centre in the Midlands, shun the theatre in favour of watching sport, and come from a working class background?

Either way you can consider yourself a member of Britain's middle class and thus the latest focus of attention for Ed Miliband – both have been used as characterisations, albeit at opposite ends of the scale. The Labour leader has described a "crisis of confidence" now gripping Britain's squeezed middle, as insecurities about jobs, pensions and the future financial wellbeing of the next generation prevail.

Following his party conference pledge to freeze energy prices for 20 months, Miliband has made a bolder promise to rebuild Britain's middle class, writing in Monday's Daily Telegraph: "The greatest challenge for our generation is how to tackle a crisis in living standards that has now become a crisis of confidence for middle-class families.

"The cost-of-living crisis is not just about people on tax credits, zero hours contracts and the minimum wage. It is about millions of middle-class families who never dreamt that life would be such a struggle."

Research suggests membership of Britain's middle class depends on personal perceptions as well as incomes.

Around 36% of Britons consider themselves to be middle class, says pollster Ipsos Mori, and they are more likely to name the economy, education and healthcare as important issues for the country than those who consider themselves to be working class.

"The middle classes are both mythical and vitally real to British politics," said Ben Page, chief executive of Ipsos Mori. "Strictly they are now the majority of the population and contain more swing voters than any other group. But they are very diverse and the great British class system means they are by no means homogenous and contain increasing divergent groups. The upper middle classes are accelerating away from the lower middle classes for example."

The middle household income – after benefits but before tax – for a couple without children living in Britain is around £30,000, rising to around £40,000 for a couple with two children, and is lower than people might expect, according to Resolution Foundation, which produced the figures.

James Plunkett, director of policy at the thinktank, said people have adjusted their expectations over the course of the financial crisis and perceptions about what makes a household middle class have also shifted.

"Ordinary working households have had an unusually difficult five years. Historic falls in wages have run alongside spikes in the price of essentials and some important aspirations, like home-ownership, have moved beyond reach.

"It now seems likely that the politics of living standards will heat up as growth returns, with all parties wanting to show they have a plan to make sure growth feeds through into rising incomes." A study by academics from the London School of Economics and the Universities of York and Manchester and published by the BBC last year, claimed that Britain now has seven social classes. According to the Great British Class Survey, 46% of Britons belong to the "established middle class", the "technical middle class", or a group of "new affluent workers".

The study analysed not only an individual's "economic capital", but also their "cultural capital" – interests and activities – and "social capital" – the number and status of the people they knew. Ed Miliband is appealing to individuals' broad aspirations, promising that under Labour people will regain the right to expect job security, affordable home ownership and secure pensions, all of which have been undermined in recent years.

In doing so he is appealing to a middle class state of mind, at a time when the financial goalposts have shifted.