Fear of the British National Party is being used as a weapon in the battle over the future of Britain’s voting system, writes Political Editor Jonathan Walker.

The debate over whether Britain should change its voting system has become increasingly ugly with both sides claiming their opponents are unwittingly aiding the BNP.

Labour leader Ed Miliband joined high-profile Liberal Democrat Charles Kennedy and Green MP Caroline Lucas to officially launch the campaign in favour of change this week.

There’s little more than a month to go before a referendum on May 5, when voters will be asked whether Britain should ditch the existing “first past the post” system and use the “alternative vote” (or “AV” for short) instead.

But as they battle to persuade voters – or perhaps to attract their attention in the first place – both opponents and supporters of change are playing the BNP card for all its worth.

At a briefing in Westminster the day before the “yes” campaign launch, opponents of the new system published figures suggesting it would give BNP supporters multiple votes in many constituencies.

In Solihull, BNP supporters would effectively get three votes, according to the “no” campaign.

The same would be true in the Birmingham constituencies of Yardley, Selly Oak and Edgbaston, they claimed.

Matthew Elliott, the campaign director for the “No” campaign, said: “A ‘yes’ vote to the unfair and expensive alternative vote on May 5 is a ‘yes’ to unequal votes and a ‘yes’ to giving BNP supporters more power at the ballot box.

“One person, one vote isn’t just the bedrock of the British voting system, it is a principle which has become a beacon to the rest of the world. The alternative vote threatens that principle.”

The logic behind his claim is that the alternative vote system allows the public to rank candidates in order of preference – one, two, three, four, five and so on.

In some constituencies, the votes of people who support minority parties will be transferred to their second preference and possibly their third or fourth as well.

By contrast, if you vote for one of the major parties then your vote may never be transferred. For example, the Conservatives and Liberal Democrats are neck and neck in Solihull, so if you vote for either of these parties then your vote is unlikely ever to be transferred to its second preference.

According to the “no” campaign, this gives BNP supporters more votes than supporters of major parties.

Whether their claim makes sense depends partly on whether you believe that having a second or third preference counted is the same as voting two or three times. And it’s also worth remembering that whatever applies to BNP supporters could apply equally to supporters of other smaller parties.

Soilhull’s MP, Liberal Democrat Lorely Burt, is campaigning in favour of the alternative vote system. She said: “I find it stunning that they are claiming it will somehow help the BNP.

“The ‘no’ campaign is running a nasty campaign, because frankly they don’t have any good arguments.”

But it has to be said that the “yes” campaigners are also happy to raise the spectre of the BNP.

They point out that the far right party and its leader, Nick Griffin, are against changing the system – and argue that introducing the alternative vote could actually keep the BNP out.

Katie Ghose, chairman of Yes to Fairer Votes, said: “AV is one person one vote. The difference is you get a vote that really counts and more of a say on who your local MP is.

“The BNP is actively campaigning for a no vote. AV is an anti extremist system because it means all politicians will have to reach out to 50 per cent of voters.

“Whenever Nick Griffin’s party has sneaked into our town halls they’ve been opposed by the vast majority of voters. He knows that extremists have no future with AV.”

Next page: How the different voting systems work >

How the Alternative Vote and First Past The Post work

Under the proposed replacement for first past the post, the UK is divided into constituencies and each constituency returns one MP.

Instead of placing a cross next to a single candidate, voters rank candidates in order of preference by writing numbers next to their names (although they are still free to mark only their first choice if they like).

If any candidate is the first choice of more than half of voters, then they win.

But if nobody gets 50 per cent of first preferences then whoever came last is eliminated from the contest.

If the people who chose this candidate as first choice also put down a second choice, then their votes are redistributed to whoever they placed second.

Once again, all the votes are counted, to see if anyone now has a majority. If not, whoever is now last is eliminated, and their votes are redistributed. The process continues until somebody has a majority.

Voters can pick any candidate as first choice in the knowledge that their second, third or fourth choices might also be counted, although it is not certain that they will be.

The winning candidate is more likely to have the support of 50 per cent of voters, but only if receiving a second or third preference is considered to indicate support. If a significant proportion of voters choose not to indicate a second preference then the winning candidate may still be elected without a majority.

A candidate can lose even if they get more first preferences than anyone else. It won’t always be immediately obvious why the winning candidate is the winner.

Some voters will find their second, third or later preferences are taken into account. Other voters will not. Opponents of AV say this is unfair.

Critics claim that expensive computer equipment will be needed to count the votes. Supporters of AV say votes can be counted by hand, just as they are today.

Voters place one cross next to the name of their favoured candidate, and whoever gets the most votes becomes the constituency’s MP.

It’s easy to understand and easy to see why the winning candidate won.

Opponents say it often forces people to vote tactically because they know they have to back a frontrunner.

For example, a Labour supporter in a seat where the Conservatives and Liberal Democrats are in the lead can vote for the Labour candidate, but their vote will then be “wasted”.

Alternatively, they could try to influence the result by voting Lib Dem or Tory, but this means they are not voting for the candidate they actually support.

What’s more, the winning candidate might be backed by fewer than half of voters.

In Birmingham Hall Green, for example, Labour’s Roger Godsiff was elected with just under a third of votes.