Jeremy Corbyn has insisted that Labour is trying to speak for "100% of the people" in the country.
The Labour leader said he believed his party's campaigns on health, education and manufacturing would get a "great deal" of support.
His comments come after a left-of-centre think tank wrote off Labour's chances of a majority at the 2020 general election and may pick up just one-in-five votes nationally.
Mr Corbyn told the BBC: "We are fighting, as a party, to protect and defend our NHS, to expand social care in our society, to properly fund education and for investment in infrastructure for a growing manufacturing economy in Britain.
"That is the appeal we are putting out, that is the appeal that I believe will get a great deal of support.
"This is an issue that faces the whole country and Labour is trying to speak for 100% of the people in this country to ensure that those policies are understood."
Asked about his own position, Mr Corbyn said: "I have been elected to lead this party by over 60% of the votes of members and supporters of this party. It is a great honour and a great responsibility.
"I am carrying out that honour and that responsibility and our party is working very hard on these issues."
Recent analysis by the Fabian Society think tank suggested that Labour is likely to win between 140 and 200 big city and ex-industrial constituencies on as little as 20% of the vote, which would be a further decline from the 231 seats it currently holds, meaning it would have to rely on a coalition in order to govern.
Mr Corbyn said: "We are campaigning on the issues of inequality and injustice in this country.
"We have a Government that is more interested in cutting corporate taxation, lowering the tax rate for the very richest and, at the same time, underfunding local authorities in social care and so many other areas.
"For the first time for, probably 30 years, school budgets are falling, our NHS is in crisis, we are campaigning on all of those issues.
"We want real social justice in this country so that there isn't a postcode lottery on when you are cared for, if you are disabled or elderly.
"We want a society that actually cares for everybody.
"That's what the Prime Minister said she wanted on the steps of Downing Street when she assumed office.
"The problem is that since then there has been further tax cuts for those that could pay more and there's been huge cuts in social services as a result of the underfunding of local government.
"Labour is on the side of people wanting decent, good quality public services and an economy that invests for the future."