DAVID Cameron has warned voters that the worst possible outcome of the General Election would be a Labour government propped up by the SNP as he made clear there was an economic, moral and practical case for tax cuts following the May 7 poll.

Speaking in the Lib Dem/Tory marginal seat of Eastleigh near Southampton, the Prime Minister also suggested he would be willing to take part in the TV leaders' debates but threw up another possible get-out by saying that if minor parties were to be included, he saw no reason to exclude Northern Ireland's Democratic Unionists. "I don't seem to know why Northern Ireland is missing out; because as far as I'm concerned that is as much an important part of the UK as Wales or Scotland."

Referring to more indications at the weekend that First Minister and Nationalist leader Nicola Sturgeon might be willing to do a post-election deal with Ed Miliband, Mr Cameron told a gathering of the local Tory faithful in Bursledon Community Centre: "If there was anyone who thought the worst possible outcome of the election was an Ed Miliband-led Labour government, actually I can now tell you something that would be even worse, and that is Ed Miliband in Downing Street, supported by the Scottish National Party who want to break up our United Kingdom. The battle of this election has become even more important."

The PM's warning of a Lab-SNP alliance was met with groans from his audience. He later warned of the "dangers and risks" of the minor parties like the SNP.

Launching another pillar of the Conservatives' manifesto, the party leader focused on tax and the promise of a £7bn cut as a "reward" for the nation's sacrifice during the recession. However, once again there were no details as to where the money would come from other than from the proceeds of growth.

But he pointed to the Coalition's record of reducing the deficit while simultaneously cutting taxes.

"Under this Government, we've cut the deficit. We've had to make difficult decisions on spending to do that. But we have cut income tax at the same time and we can do it again in the next Parliament."

Mr Cameron confirmed plans for a further £30bn of spending cuts if Tories won power in May, including £13bn from Whitehall department spending, £12 bn from welfare and £5bn from cracking down on aggressive tax avoidance.

"After the security of a job, the next best thing we can do is to cut people's taxes and let them keep more of their own money to spend as they choose. That's our aim."

He said there were three very good reasons for cutting taxes. The economic one was that a low tax economy was successful, rewarding effort and enterprise, and making Britain more competitive. The moral one was that it was right to leave people with as much of their own money as possible to spend as they liked. The practical one was it provided security.

The PM restated promises made at last year's Conservative conference to raise the personal allowance threshold below which workers pay no income tax to £12,500, which would take another million people out of paying tax altogether, and to "back aspiration" by increasing to £50,000 the level at which the 40p tax rate kicks in, taking out 800,000 people out of that rate.

Mr Cameron said May's election offered a choice between "whether we have a government with competence, with grip, with a long-term economic plan, or whether we have the chaos of Ed Miliband in Downing Street and all that would mean".

Meantime, Jonathan Isaby, chief executive of the TaxPayers' Alliance pressure group, said: "The Prime Minister is right to commit to lowering taxes on hard-working people and all leaders should be looking to make similar pledges.

"However, Mr. Cameron's commitments aren't quite as generous as they first seem - he is not planning to raise the 40p threshold quickly enough to keep pace with inflation and, while a further increase in the personal allowance would be welcome, he has said nothing about what he would do with National Insurance, which is a second income tax in all but name."