A future Labour government would take legal steps to ensure that live television debates become permanent features of general election campaigns, in a move to prevent politicians blocking them for their own self-interest.

After weeks of deadlocked discussions that have seen David Cameron reject the broadcasters’ offers of a head-to-head debate with Ed Miliband, the Labour leader said he would act to ensure future TV debates could not fall victim to political pressures, but would be enshrined as a statutory right of voters.

The Observer has learnt that a Labour government, in a significant constitutional move, would put the requirement to stage “fair and impartial leaders’ debates” on a statutory footing. The new system would work on similar lines to the current rules for planning the number, length and timing of party political broadcasts, under which parties are consulted but not given the power to stop them happening. This could be done by establishing the body which negotiates the terms of debates as a trust in statute with responsibility for determining the dates, format, volume and attendees.

A Labour government would set a deadline of 2017 for changes to be put in place, giving more than enough time to plan the debates for a 2020 election.

Confirming the move, Miliband told the Observer: “In recent days the British public has been treated to the unedifying and tawdry spectacle of a prime minister seeking to duck out of the TV debates he once claimed to support with great enthusiasm. Yesterday the broadcasters made it clear they would not be cowed by his tactics but it is wrong for them and the British public to have governing parties use this kind of pressure in campaign periods. It is time to ensure, once and for all, that these debates belong to the people not the prime minister of the day.”

Tory insiders say Cameron is determined to avoid appearing on TV on equal terms with Miliband before the 7 May election, as he believes the Labour leader, whose ratings are far lower than the prime minister’s, is the only one who could benefit. Chief election strategist Lynton Crosby and the former party deputy chairman Lord Ashcroft both insist Cameron should not risk taking part in a head to head, even if he endures short-term criticism for not doing so.

Last night Vernon Bogdanor, professor of government at King’s College, London, and author of The New British Constitution welcomed the Miliband plan and said: “The public are entitled to see how party leaders perform in debate, and also how the PM and alternative PM perform – they cannot judge this from PMQs which have become a national embarrassment. Debates should not be subject to the tactical calculations of party leaders. That is the case for a statute requiring debates between leaders of all parties with over 5% of the vote; and a separate debate between the PM and leader of the opposition. That statute is best administered by the Electoral Commission, in my view, rather than the broadcasters who can too easily be accused of bias.”

The BBC, ITV, Channel 4 and Sky want three planned debates: a head-to-head between Cameron and Miliband and two involving seven party leaders.

Cameron has refused to take part in the head-to-head and has said he will only take part in one debate involving all seven leaders, if this is held before the campaign proper begins in April.

The four broadcasters announced on Friday that despite the prime minister’s rejection of their plans, they would stick to their guns and nonetheless hold the debates. They also urged the prime minister to “reconsider”.

But Cameron’s chief spin doctor, Craig Oliver, said their response was disappointing and restated that the prime minister’s final position was for a single debate in the week starting 23 March. This opens up the prospect that Cameron could be “empty chaired” in the head-to-head debate.

Addressing Labour’s Scottish spring conference on Saturday, Miliband said: “He [Cameron] says this election is all about leadership, all about the choice between him and me, and when it comes to a debate between him and me, he’s running scared. You can try to chicken out of the debates, but don’t ever again claim you provide strong leadership.”