There’s a rude word that won’t appear in this column. As a child your columnist was taught to avoid it. The word begins with l, and the three-letter version means untruth. The four-letter version describes someone who habitually tells untruths. These terms should hang in the air, on the tip of my argument’s tongue, tantalisingly unarticulated. They should hang unvoiced, too, above the figure of our present Prime Minister.

“In every year in the future,” said Gordon Brown on June 5, “public spending will continue to rise.”

There are a number of things that statement wasn’t. It wasn’t a half-truth. It wasn’t an evasion. It wasn’t a distortion. It wasn’t a sleight-of-hand. It was a far, far simpler thing. It was a flat . . . you know what. Mr Brown’s apologists (their population crashing towards extinction) mutter wretchedly that their master was talking in “cash terms”. In “cash terms” the basic state pension, which was introduced in 1909, would now be 25p per week. If Mr Brown knows anybody who wouldn’t in plain English call that a cut, let him name them.

And when you realise that the projected cash totals on which Mr Brown was basing that . . . fib . . . also include the ballooning costs of our national debt, and of bankrolling a growing army of the unemployed, it becomes even clearer that the impression he meant his hearers to gain — that there would be more in the kitty for things like schools and hospitals — was a barefaced . . . misrepresentation.

Then there was Prime Minister’s Questions last week. I’ve had to check this in Hansard because, astonished, I lost confidence in my own recollection. Mr Brown said: “Capital expenditure will grow until the year of the Olympics.”

The London Olympics is in 2012. Capital expenditure is most assuredly not projected to grow until then. It is peaking now, in the present financial year, and will start falling in the next financial year — very substantially. Mr Brown said so himself seven days later at PMQs this week. He said that “capital investment [has risen] to £44 billion in 2009-10 . . . [reader, please note these dots] . . . Thereafter it will fall as a result of decisions that we have made.”

Do you know any way of reconciling Mr Brown’s earlier mis-statement with a continued belief in his own truthfulness? Actually I do. Maybe he just made an innocent mistake the first time round. In that case his restatement of the position this week could have been meant to acknowledge the mistake and set the record straight.

Dream on. Or shatter the dream by permitting me to fill in the triple dots which, in that extract from Hansard above, I asked you to note. Here it is again, but with the missing bit in italics:

“The Prime Minister: . . . capital investment [has risen] to £44 billion in 2009-10, and that is to help complete the building of the Olympics. Thereafter it will fall . . .”

What a snivelling, broken-backed little attempt at a wriggle-out. Caught in the act of telling a complete . . . whopper, unwilling to admit or apologise, and with nowhere to hide, Mr Brown attempts a new dishonesty: trying to suggest that because the high figure this year includes a lump of spending on something (the Olympics) that won’t be happening until 2012, you could sort of spread the lump forward into the figures for the whole pre-Olympic period, and make the graph continue uphill.

At this point, in any criminal court, the judge would explode with impatience, cut short counsel for the defence and direct the jury to convict. It won’t do — as David Cameron immediately responded this Wednesday.

But Mr Cameron has a trickier task ahead than may be apparent. A desperate man, Mr Brown is now so entirely shameless that he’s planning to keep . . . dissimulating about “Labour investment” versus “Tory cuts” in the hope that the stupid or ignorant will believe him, and the rest will despair of pinning him down and move on.

So should Mr Cameron simply hope that the Opposition have made their point, and change the subject? Or should he act the club bore and hammer tediously on about the Government’s failure to acknowledge either the mess we’re in, or the spending cuts that are thundering towards us like a runaway train?

He should hammer on. He must bore for Britain. This is so much bigger than any other question facing the nation, so much more urgent, so much more disgraceful, so much more likely to impact on all our lives for a decade to come, that for Mr Cameron to turn aside from the issue in exasperation as Mr Brown fibs, and fibs, and fibs, and persistently refuses to look Parliament or the country in the eye, would be a dereliction of an opposition leader’s duty. It would also miss something about the way the country is feeling: something Mr Brown himself has utterly missed. Britain is ready to think about cuts, even if Mr Brown isn’t ready to talk about them.

Mr Cameron need have no fear of this issue. Even in Mr Brown’s own Cabinet, opinion is moving away from making this the “dividing line” with the Tories. Were I the Tory leader I’d be more worried about the trivial but incendiary issue of MPs’ outside earnings, with which Mr Brown intends to start making mischief soon.

The PM will find this easier. He plans to wrong-foot the Tories with one of his typically itsy-bitsy proposals for a graduated clamp on outside earnings. The Tories must accept that the public mood on second jobs may be wrong, but is strongly against them. They will have to give ground. Mr Cameron should pre-empt the attack with a bold and simple proposal. Starting in the next Parliament (and whatever the rules state) Tory MPs should share with the electorate the proceeds of outside work. I’d propose a 50:50 division, after tax. That way, voters would benefit from their investment in a high-earning MP. We might even get Ken Clarke free.

This would hurt, but it would maintain the principle that backbench MPs may keep links with the world of work outside politics; it would acknowledge (what is true) that it is for their political status that many outside-earning MPs are employed (I exclude the dentist, Sir Paul Beresford MP); and it would kill the controversy. But that’s for another column, another day.

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