First year law students learn a very basic principle the minute they cut their teeth in the theories of the trade: he who asserts must prove.

The rationale behind it is simple; to ensure that no one is convicted of an offence - or is defeated in a civil court - unless there is evidence to back up the claim being made. It is by having established principles of this nature that a civilised country is distinguished from Hobbes' jungle.

But this benchmark is not just applied to the courts. In our every-day lives we rely on what we consider to be authoritative sources - depending on the nature it could be our families, neighbours or the media - to provide us with information. And, if asked to do so, we ask them to prove to us that what they state is correct.

The media, at least the ones serious about their business, are rightly expected to rigorously investigate an issue, and have proof at hand, before daring to put it in print or on the airwaves. And we should expect nothing less from our politicians.

So when the Labour Party erects an electoral billboard stating, with no room for ambiguity, that the large majority of the Cabinet is corrupt - an assertion that would not see the light of day in most other European countries - it is only reasonable to ask to see the evidence to back up that claim.

In the interview with Labour leader Alfred Sant today, The Sunday Times asked him, quite reasonably, for precisely that. "We'll show it if people ask us for it," he said. So the interviewer retorted: "I am asking you. Can I see it?" To which the vague reply came: "It's well known all over the place." The interviewer tried again: "If I ask you that I'd like to see this evidence of corruption, would you give it to me?" Dr Sant responded: "It's not evidence. It's something people know."

So, when pressed, the Opposition leader makes a damning implicit admission: that he is making statements which undoubtedly damage people's reputations without having any-thing but gossip and hearsay to back them up.

This is not acceptable in pub conversation, let alone on the political platform. Yes, libel suits may follow. But they will not be resolved within the next two weeks. And he knows that.

However, it is not just on serious accusations that Dr Sant is having a problem with evidence. He is groping in the dark on policy aspects too.

When asked how he will pay for his proposal to halve the water and electricity surcharge irrespective of the price of oil, Dr Sant responds, "from the public budget" - even if it rises by 1,000 per cent.

Yet he fails to say where from - other than speculating that the economy will start growing by six per cent - or guarantee that he will not introduce another tax to compensate for slashing the surcharge.

Nor can the Opposition leader offer any evidence that he can renegotiate new conditions with the EU for the dockyards and agricultural sector, as he has promised voters.

In fact, the EU has made statements to the contrary, saying that matters already contained within the Accession Treaty cannot be re-opened. Which is just as well, since people have been eating the proof of that particular pudding for the past four years.