AT times last year it seemed no meaningful television debates would take place before the election.

Since the end of March, however, we have seen have seen a whole series of programmes, each with a different format and line-up.

Four have been UK-wide: Sky and Channel 4 shared the "Battle for No 10" interviews, involving just David Cameron and Ed Miliband; ITV held a seven-way leaders' debate, and the BBC staged a "challengers' debate" followed by last week's Question Time special.

BBC Scotland screened the third and final debate to feature Scottish party leaders Nicola Sturgeon, Jim Murphy, Ruth Davidson and Willie Rennie.

Across all the debates, Ms Sturgeon has come out on top thanks to a string of polished performances which have sealed her emergence as a major UK politician. Ed Miliband has done well, while David Cameron has not suffered as badly as the Conservatives feared.

Would the final Scots debate change anything? Would it be an afterthought or might someone land a killer blow with only four days to polling day?

Presenter Glenn Campbell clearly feared an all-out rammy and made the four leaders promise in advance to conduct a "respectful debate".

His entreaty was respected for all of 15 minutes, until the question of welfare cuts was posed.

When Mr Murphy accused the Conservatives of docking claimants' benefits unfairly, Ms Davidson exploded, telling him: "That's an outright lie, it's a falsehood. He is making it up."

Mr Murphy hit back: "How dare you call me a liar."

Moments later, when Ms Sturgeon claimed Labour had backed cuts to disability benefits planned by the Conservatives, Mr Murphy retorted: "It's just not true."

Under pressure over her plans for full fiscal autonomy, which the IFS think tank has warned would blow a £7.6billion hole in Scotland's finances, Ms Sturgeon reached for the same familiar rebuttal.

"It's made up. This is a myth on the part of a rather desperate Labour Party," she protested.

In truth this was a tetchy debate between four candidates who all looked slightly too tired to be at their best.

If viewers did not switch off during the rancorous exchanges over welfare, they probably dozed off when the debate moved onto housing policy towards the end.

But those who watched the middle section of the show, broadcast from the splendid Mansfield Traquair in Edinburgh, saw some important clashes on the issue that is really exercising voters: what might happen after May 7 if there is a hung parliament.

Ms Sturgeon's threat to vote down a minority Labour government's budget, if she felt it failed to end cuts for the poorest, will set up three furious final days of campaigning.