Vince Cable: No wonder the Tories are so scared of AV

It is only self-interest and the desire to have things their own way that makes the Conservatives so keen on first past the post

The importance and seriousness of Thursday's AV referendum have been obscured by scratchy, bad-tempered debate. But the edginess of the campaign tells us something: there is a lot at stake, politically.

A change could have major consequences. AV recognises that we now live in a world of multi-party politics and makes it easier for voters to express a wider range of choices. It will encourage prospective MPs to reach out beyond a narrow party base for wider support in the form of second preferences. Coalition is not a necessary consequence of AV, but it is more likely that parties will have to work together in government.

AV undoubtedly poses a threat to the old tribal politics and to the Conservatives in particular, who have been best able to exploit it to advantage. The forces of reaction have been impressively marshalled on the battlefield. Not a single Conservative parliamentarian has broken ranks in an uncompromising defence of the status quo. The country's right-wing newspapers – both the Murdoch and non-Murdoch titles – have swallowed their dislike of the coalition's liberal compromises, and of each other, to line up solidly behind the No campaign.

They understand all too clearly where their political and financial interests lie: in a system which enables them to rule most of the time with minority support.

The legitimacy of the current system was already under threat from the voters. Some 35.5 per cent of voters no longer vote Conservative or Labour – despite being told, in many cases, that their votes are "wasted". I grew up in a two-party world and the voting system reflected political reality. More than 90 per cent of MPs were elected by a majority of their voters. But that proportion is now down to about a third. Where there are three parties in contention (four or more, in Scotland, Wales and Northern Ireland), voters adapt to the system by means of tactical voting: supporting the candidate whom they dislike least rather than the one they want. I have personally progressed from being a victim of tactical voting to a beneficiary of it, but, even as I use the system to advantage, I know that it diminishes democracy. The voting system should meet the needs of voters, not the other way round.

The AV system still falls some way short of fully proportional representation or the proposal (AV plus) advocated in the (Roy) Jenkins report a decade ago and now employed in Scottish parliamentary elections. But it is counterproductive to reject the good because it is not the best. Moreover, the AV system defers to two genuine concerns in public opinion. One is that MPs should retain a direct link to their constituencies rather than have an exclusive dependence on their parties. Indeed, AV will make it easier for independent-minded MPs to defy party whips. They can appeal to their constituents over the heads of party bosses without splitting the vote (as Ken Livingstone successfully did in his first run for London Mayor – on a variant of AV).

The second concern is "opening the door to extremists" which can happen with pure proportional representation, as in Holland or Israel. One of the more dishonest claims of the antis is that AV will help the BNP. It will not. Fascists will find it extremely difficult to attract 50 per cent of the vote anywhere. BNP cadres may not have the sharpest political brains but even they have worked out that while their chances of a breakthrough are currently small, under AV they are virtually nil – which is why the BNP opposes AV.

A big psychological threshold for electoral reformers to cross has been the fear that reform means coalitions and weak, indecisive government. One of the ironies in this whole debate is that it is a coalition government which has delivered a referendum on electoral reform. And the same coalition has totally demolished the claim that coalition means weak government. Its very decisiveness has created enemies who find it difficult to see beyond their enmity. AV probably does mean more coalition. And coalition does involve shedding the baggage of tribalism. Former opponents have to work together on a common programme. I currently work with George Osborne to deliver a credible economic policy. Even more improbably, Martin McGuinness and Ian Paisley have worked together to deliver peace in Northern Ireland. Labour worked with the right-wing enemy, Winston Churchill, in wartime. In Scotland and Wales, parties are working together, locally and nationally, while competing at Westminster.

This is grown-up politics. But tribal loyalists hate it. There is a real danger that because of factional dislikes on the progressive side of British politics we shall again miss a historic opportunity. Wiser counsels, such as Ed Miliband and Alan Johnson, can see the big picture, but others cannot see beyond short-term, party point-scoring.

Let us remember what the big picture is. The last century produced two great reforming governments in 1906 and 1945. The Liberals created the old-age pension and the People's Budget was forced past the House of Lords, over the screams of the rich and powerful. Clement Attlee's government rebuilt a shattered economy, advanced the programmes of Beveridge and Keynes and launched the NHS, which progressive politicians still rally to defend. But these governments were brief interludes of sunlight in a grey Conservative- dominated century. The pattern could easily be repeated. From time to time Conservative governments will and should be elected when they reach out for a majority of voters. The AV system will not stop them. What it will prevent is repeated unrepresentative government of the right.

Labour, Lib Dem and Green supporters should ask themselves one simple question before they vote: why is it that the Conservatives are pulling out all the stops, with their millionaire backers pouring the contents of their coffers into the No campaign? It is because they know that the first-past-the-post system is stacked in their favour and they are determined to keep it.

Vince Cable is Business Secretary and Liberal Democrat MP for Twickenham