Past, present and future

She was there, she said, "to discuss an RBS banker who enjoyed huge success but whose arrogance drove him to over-reach himself and lead Scotland to disaster".

Cue wry grin from Johann Lamont. Her intention, she clarified, was not to focus upon the former Royal Bank economist before her (Salmond, A., FM) but rather the former boss of the bank (Goodwin, F., ex knight.)

It was rather an effective opening gag - and also signalled Ms Lamont's intention to link two issues: the past banking crash and the future of Scotland.

But why would the Labour leader be so keen to pursue the issue of ex-Sir Fred? Why especially when, as Alex Salmond pointed out, he was knighted apparently at the prompting of Jack McConnell, and called upon for advice by Gordon Brown?

Perhaps that blend of issues noted above gives us the clue. Firstly, Ms Lamont believes she can taint Mr Salmond personally by association with Mr Goodwin.

Secondly, the royal bank has now become a totem of the banking crash, of economic uncertainty.

Consequently, it can be deployed by supporters of the union as shorthand for suggesting that Scotland could not survive as an independent nation.

The rebuttal from Nationalists is that the failure of banking regulation occurred on the UK's watch. Mr Salmond deployed said argument today.

But back to Ms Lamont. Her predecessor occasionally noted that it could be difficult to sustain one topic over the multiple questions afforded to the leader of the largest opposition party.

Ms Lamont obviated that problem today by skipping between two topics: banking and independence.

As suggested earlier, her intention was to suggest that the common thread between the two topics was poor judgement on the part of the FM.

Indeed, her entire assault was designed to build to the crescendo of claiming that Mr Salmond had become "the Fred Goodwin of Scottish politics."

On the day, it was rather well contrived - and certainly attracted supportive guffaws from her own backbenches.

But it strikes me it remains somewhat contrived, an oratorical conceit rather than an intellectual argument which can be sustained.

Still, this was a sparky series of exchanges: insult, argument and wit on both sides.

For her part, Ruth Davidson, of the Tories, pursued the issue of defence: jobs, contracts, the role of the armed forces, post independence.

She read a letter from an unnamed Scots soldier, seemingly distressed at the prospect of having to choose, under independence, between his current British service loyalty and the nation of his birth.

At least, Mr Salmond retorted, he would have a choice - by contrast with service personnel who were being made redundant under UK government cuts.