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Neither side in the Alternative Vote (AV) referendum campaign may yet have established a crucial breakthrough.

Indeed what both sides agree on is that with at least a third of voters undecided, and many others probably confused or just plain uninterested in the referendum, the result remains highly unpredictable.

But within the No campaign there is a view they have one key argument which could swing the debate their way - Nick Clegg.

In short, if the referendum could be turned into a vote on Nick Clegg then many voters, it is thought, would use it to give the Deputy Prime Minister an electoral kicking.

Within the No side however there is some caution about how far to play the Clegg card.

Some fear it would be seen as "going negative", while others fear it might even rebound against them and lead to sympathy for Mr Clegg.

There is also a concern that the prime minister might be less than amused to see his coalition partner publicly rubbished by a campaign he is backing.

And yet the temptation to play the Clegg card is huge.

James Frayne, who ran the successful No to a North East Assembly campaign said: "He is associated with everything that people currently distrust about politicians. It may be unfair but that is reality."

The No campaign, he suggested, should be "all over him" if they want to win.

The reason for this is because strategists have identified Labour voters as the people who will determine the outcome of this referendum.

Most Tories will naturally back the existing First Past the Post system. Most Liberal Democrats will vote for AV.

The Labour vote - like the Parliamentary Party - is split.

However pollsters believe the No campaign could win over large swathes of Labour voters if they could convince them that a vote for AV was a vote for Nick Clegg.

Andrew Hawkins of the pollsters ComRes said: "Clegg could definitely be a decisive factor."

Privately the No team say they will make Nick Clegg an issue in this election, by arguing that AV will lead to permanent coalition government which will lead to a permanent place for Mr Clegg around the Cabinet table.

But how hard, and how personal, they choose to make the attack on Nick Clegg, remains to be seen.