Nick Clegg today makes a bold pitch to Labour voters, claiming that the Liberal Democrats have supplanted Gordon Brown's party to become the natural home of progressive politics in Britain.

In a Guardian interview, Clegg accuses David Cameron of having no agenda for progressive reform of the country, and says the Lib Dems and Labour come from the same historical tradition.

He says he is rejecting all talk of tactical voting and is instead "going for broke" to maximise his party's share of the vote.

Clegg insists that the tectonic plates of politics are shifting, and the choice has distilled down to a vote for his party or a Conservative party that will "cast the country adrift".

The Lib Dem leader appears to suggest that any post-election arrangement with the Tories would be a coalition of convenience rather than principle when he asserts: "There is a gulf in values between myself and David Cameron," adding: "They have no progressive reform agenda at all – only an unbearable sense of entitlement that it's just their time to govern."

During the two years of his leadership, Clegg has successfully maintained a position equally distant from the Labour and Conservative parties, but today he emphasises that the Liberal Democrats have shared progressive history.

His remarks go further than before in suggesting that if he feels the electorate has given him a choice, his instinct will be to form an alliance of some form with Labour. He holds out no hope of securing electoral reform from Cameron.

He says: "What is striking is despite all the blather from Cameron over the past few weeks, he has made up his mind strategically to set his face against any profound reform of the political system. I think this will prove to be the biggest strategic error he has ever made, because one thing you cannot do is set your face against change when the demand for that change is so powerful that it is coming from millions of people.

"In terms of its DNA, the Conservative party is now the party of entrenched vested interests of politics."

Saying that he is now aiming for more than 100 gains on the party's 63 MPs, and even the largest share of the vote, Clegg says: "I don't think the choice is between Conservative and Labour – the choice is now between the Conservatives and Liberal Democrats." Clegg's hopes of gaining more than 100 seats were confirmed by a Harris poll of voting intentions for the Daily Mail today, which put the Conservatives on 33%, the Lib Dems on 32%, and Labour in third place with 24%. If this poll result were reflected in the election, it could give the Lib Dems 137 seats.

While many progressives are calling for anti-Tory tactical voting by Lib Dem supporters in the key 100 Labour-Conservative marginals, Clegg rejects this advice.

He argues: "In an election where the tectonic plates are moving so quickly and so radically, people have got to go with their gut instincts. Once in a while there are elections where people should be released to do what they want, and I think this is one of those elections – I really do." He denies this shows he is willing to put his chance of overtaking Labour ahead of preventing a majority Tory government. "The Tories are nowhere near getting an overall majority. We are absolutely going for broke so far as the share of the vote is concerned."

He also makes it hard to see the basis of a Tory-Lib Dem coalition. "I think if you look at the debate last night, there is just a gulf between what David Cameron stands for and what I stand for – in terms of values, in terms of internationalism, in terms of fairness, in terms of progressive tax reform, in terms of political reform, in terms of simply living in denial, as does Labour, about a major problem of their creation in the immigration system."

Asked if the same gulf existed with Labour, he says: "I have always accepted the first part of Roy Jenkins's analysis which says that historically Labour and Liberal Democrats are two wings of a progressive tradition in British politics." But Clegg maintains his party cannot be an annexe of Labour, and there is a fundamental difference between the two parties over the individual and the state.

"There are some people in the Labour party that now get [it that] progressive politics has to be about empowerment, reducing dependency on the state, increasing social mobility through individual empowerment, releasing power from the centre politically – but it is not where the Labour party lies at heart. Listen to Gordon Brown's final message last night – it was: 'You're not allowed to take a risk on anyone else.' It's a very dismal, cramped and depressing message. That's why polls are putting us ahead of Labour, and that'll crystallise in the next few days into a two-horse race." Clegg insists that politics has been changed permanently by this election.

"I personally think both the Tories and Labour face profound crises of identity because they are both based on assumptions of mass support that have now evaporated. The arrogance of both the Conservative and Labour party that it's somehow their birthright to speak on behalf of millions of people. That's gone."