Analysis By Nick Assinder Political Correspondent, BBC News website

If you are going to cast yourselves as the "real alternative" to Labour and the Conservatives then you are going to have to spend some real money.

Kennedy wants positive campaign

So Charles Kennedy's Liberal Democrats have done just that with the most expensive ad campaign in the party's history.

And it has probably come at just the right time in the phoney election war which has been escalating over the past couple of weeks.

The danger for the Lib Dems is always that they will be squeezed out of the frame as the two big parties start knocking chunks out of each other.

And it is certainly the case that the last few days have seen attention focusing onto the increasingly bitter row between Labour and the Tories.

It is widely believed that the Tories have snatched the agenda with a series of assaults on areas including the NHS, immigration and the war on terror.

Turned off

As a result, the Liberal Democrats must have been starting to feel the pinch. And Mr Kennedy admitted as much in his campaign press conference.

But, as the battle between Labour and the Tories has become personalised, angry and, some believe, negative, Mr Kennedy says he wants to offer a positive alternative.

And it is not just the ten reasons to vote Lib Dem, as set out in the ad campaign.

It is the style and character of the party's campaign which Mr Kennedy believes will chime more with disillusioned, disengaged voters.

Lib Dems cast themselves as real choice

He has insisted he will not engage in negative or personalised campaigning, claiming the British people are turned off by that style of politics.

He admitted that there were risks involved in this approach as it might give the other parties time to squeeze the Lib Dems - something he confessed happened in the past.

This time, however, he claims opinion polls show there has not been a squeeze on the party.

Laid back

And Lib Dem peer Shirley Williams addressed the decision, saying: "We are taking a calculated gamble on the intelligence of the electorate".

Another characteristic of the Lib Dem campaign, according to party bosses, is the emphasis on the leader.

The ad features Mr Kennedy prominently alongside the ten reasons to vote for his party.

This, they claim, is in marked contrast to the two other parties whose leaders are not being given prominence for fear of turning away voters.

Mr Kennedy's laid back, approachable style was said to have paid dividends in the last general election campaign and the party strategists clearly believe the same can be true this time around.