FIRST it was so-so, then it was dire (or so it appeared), and then, against all expectation, FMQs was something intriguing and substantial.

The so-so bit was Labour's Johann Lamont.

"Will he get on with the day job?" she yelled at the FM after accusing him of failing the NHS.

At which, Alex Salmond did get on with his day job - tearing apart Ruth Davidson.

The Tory leader's question was on the start-up costs of an independent Scotland.

Given the Treasury had just been caught making up figures, it was a dangerous ploy, and Mr Salmond could barely contain himself as she asked about his "reasonable estimate" of £250m.

Did she not know that came from an LSE academic miffed at the Treasury "badly misrepresenting" his work to claim the cost was £2.7bn?

Raising it was "basic unwisdom", he chortled.

But just as Ms Davidson's high-wire act seemed fated to end with a mop and bucket, she produced John Swinney's infamous leaked memo of 2012.

This recorded that the finance secretary had ordered a "comprehensive overview" of the start-up costs to update the cabinet.

"Why will he not let Scotland see the numbers?"

The First Minister's response was instructive. He wouldn't go anywhere near the subject.

A steely Willie Rennie then closed the jaws of a Tory-LibDem trap, pointing out the cost paper mentioned by Ms Davidson was two years old.

"Will the First Minister tell us where it is?"

The simple questions are always the best.

"Well, eh, I would say, ah," stumbled the FM.

There was a shift in the chamber's mood. Suddenly Mr Salmond was on the backfoot.

Mr Rennie pressed his advantage: Would the government publish the figures?

Rattled, the FM waffled at speed through the wonders of Yes.. £1000 a head.. fairer society.. better future.. er, what was the question?

It was a brave fist, but by the end it appeared Mr Salmond did indeed know the start-up costs, but instead of publishing them was sheltering behind the £250m guesstimate.

Even with the success of his 5:2 diet, it was too small a fig leaf to hide his embarrassment.