NO matter how hard shadow home secretary Chris Grayling tried to sound convincing, there was a little wobble in the back of his throat betraying the fact he wasn't even persuading himself.

He was trying to refute claims the Tory party had misrepresented statistics to make it look like violent crime had gone up more than it actually had under Labour.

But within seconds he began to sound like someone with a complex for being short, who stands in front of the mirror telling themselves that size doesn't matter.

Grayling had sent out figures to all Tory MPs claiming to show how violent crime had jumped over a period of time. But what he didn't tell them was, halfway through this period, the way crime was reported changed dramatically.

Firstly because more offences suddenly became classed as violent crime – including swearing at someone – and also because statisticians started including reported crime as well as recorded crime.

That meant things changed so that if someone just went up to a copper and said "I've just been bopped", this would now get into the stats, regardless of whether the claim was actually substantiated or not.

When officials at the Home Office put out the figures they added a caveat saying those before the changes could not be compared with those after, but that information seems to have been lost on Grayling.

The debacle is the latest pile of political do-do to have plopped on his once shiny head. For some reason Grayling was once known as a Tory "attack dog", wheeled out to tear into Labour plans, but in recent months it has become harder to take him seriously.

At the Conservative Conference last autumn he made an absolute humdinger of a political gaffe.

He was being asked what he thought of the appointment of ex-army chief Sir Richard Dannatt as an adviser and he replied by launching into a monologue about how it was a typical Gordon Brown gimmick.

The problem was that it was his own leader David Cameron that had appointed Dannatt. The look on his face was priceless when he had to apologise, in a voice that betrayed that all too familiar wobble.

We shouldn't be too harsh on Grayling because, actually, he isn't the only Tory who has misused figures recently.

Another release last month from the Conservative health team gushed in a press release "new figures uncovered by the Conservatives have found that the number of patients leaving hospital malnourished has risen by record levels!"

But when regional journalists inspected the figures more closely to find what was happening at their local trusts, they found the way the stats were compiled meant no such assertion could be drawn from them. In fact, the statisticians who had compiled them even put a note, helpfully saying that the figures should not be interpreted that way.

The Tories who put out the release, seemed to have overlooked the note (I even had to direct them to it) and, as a result, regional journalists dumped the story.

I might add that several of our national colleagues seemed not to question the press release so thoroughly and carried inaccurate articles the next day.

But again, we shouldn't be too harsh on one party because – surprise, surprise – both of the others put out flaky figures too.

The Lib Dems once put out a release claiming that if they got in power they would definitely solve an extra 82,000 crimes; how could they be so specific?

The answer was a ridiculous extrapolation from the number of crimes solved the previous year, compared to UK officer numbers and some extra money they'd put in, which turned out to be cash they didn't necessarily have.

Then there is Labour, who once announced a Government contract claiming it would provide, or protect, 12,500 UK jobs. Yet under closer inspection, fewer than 2,000 could really be accounted for.

Given that we are meant to be having a make-or-break debate on the state of the economy and what to do about it, the fact that all parties have displayed incompetence with numbers is worrying.

The best thing to do when you get the figures wrong is admit it, learn from it and move on.

It's the only way to stop any future wobbles.