Chris Huhne: The implicit media prejudice against the Lib Dems

They feel they can ignore a third view in the interests of adversarial debate

Jeremy Hunt, the Conservatives' media spokesman, recently accused the BBC of bias against the Tories, and bizarrely called on the corporation to hire more Conservative-inclined reporters.

A hiring policy that sought out particular views in people who are meant to be professionally impartial would be a dangerous step towards a Berlusconi-style system. It would probably be illegal under anti-discrimination law.

But Mr Hunt's premise, and hence the Tory analysis, is just wrong. The real bias at broadcasters is not against the Conservatives, but the Liberal Democrats.

The evidence of such bias is compelling and persistent. Broadcasters repeatedly ignore a third view on matters of the day. Even where Labour and Conservative views are nearly identical – such as on crime, Afghanistan or Iraq – news organisations evidently feel they can eliminate the Liberal Democrat viewpoint in the interests of simple, adversarial debate. The idea that there might be more than two points of view in an argument is normal in other European democracies, but not here.

Reporters even refer to "both parties" or "both main parties" as if we were still in the Fifties-style two-party system, which is deeply insulting to voters who do not live in Labour-Conservative battlegrounds. Forty per cent of parliamentary seats have the Liberal Democrats in first or second place.

We now live in a world in which Labour and the Tories together won fewer than half of the votes in the last nationwide election. How could the Conservatives be a "main party" in Manchester, Newcastle, Sheffield or Liverpool when they have not been able to elect an MP or a councillor for many years?

Yet the broadcasters still try to shoehorn us into a two-party debate. I recently presented the evidence for the broadcasters' systematic bias at one of David Butler's Nuffield College seminars. It comes in one simple form. In every election campaign since 1979 with one exception, the Liberal Democrats' share of the vote has gone up.

The increase comparing the average of the opinion polls in the month before the campaign and the final result is 3.9 percentage points, a large rise in electoral terms. According to UK Polling Report, this would mean 22 more MPs for the Liberal Democrats compared with the current polls.

One change explains the sudden spurt of Liberal Democrats in elections: broadcasters begin rigorously to apply a code of fairness between the parties. This ensures that coverage is not only impartial and accurate, but is also balanced between the main parties.

The result speaks for itself. When viewers and listeners are given the opportunity to hear and examine Liberal Democrat leaders, attitudes and policies, they warm to them. The campaign rise is now one of the great regularities of British politics.

The sharp-eyed will spot that I excluded one election – 1987 – from the calculation. During that campaign, support for the SDP-Liberal Alliance declined, but for an exceptional reason. The Alliance had two leaders who disagreed about nuclear weapons in the middle of the campaign. We have not made the mistake of having two leaders since.

The real bias of the broadcasters is thus not any deliberate attempt to skew reporting, but an unthinking conspiracy to remove the Liberal Democrat point of view from public debate between elections. It is bias by indifference. But such a bias more effectively undermines our support than anything else. People do not support a party they do not know.

This is particularly important when so many voters for both Labour and the Conservatives are motivated primarily by dislike of the other. In these circumstances, there could be a particularly large election bounce for the Liberal Democrats. The recent YouGov marginals poll found that 37 per cent of voters would support the Liberal Democrats if they thought we could win.

Britain's broadcasters should not prejudge the voters, let alone the electoral system. The only fair approach, at a time of heightened political sensitivity, is to apply the rules as they would be applied in the general election.

After all, both Labour and the Conservatives have recently announced their election campaigns have begun. It is time for broadcasters to begin election-style fairness too, and let the contest of ideas begin.

The writer is Liberal Democrat shadow Home Secretary