It was a speech from a man who had reached the end of his tether about what he firmly regards as SNP lies about the NHS.

Gordon Brown's moving intervention yesterday, stressing that the NHS in Scotland was under no threat from staying in the Union, invoked his own experiences of relying on the health service, including when he and his wife Sarah lost their baby daughter Jennifer at just 10 days old. Doctors could do nothing to save her, but did everything in their power; watching them, his respect for the NHS only grew. He could never stand by, he said, if he believed the Scottish NHS was going to be privatised and have its funding cut.

Mr Brown stressed that the only way health services in Scotland could be privatised was if the Scottish Government chose to privatise them, and that under existing proposals for enhanced devolution, Scottish ministers could raise up to £3bn in tax to spend on the NHS if they chose. This passionate and sincere intervention from the man who has come to be the figurehead of the pro-UK campaign is the sort of appeal that has until now been missing from the rather bloodless campaign of Better Together and is a measure of how determined the defenders of the Union are to wrest back the initiative.

It is also a measure of how critical they regard the situation to be, now that the opinion polls have narrowed so dramatically. Following Mr Brown's speech yesterday, the three main UK party leaders are all today heading north of the border in a show of unity; Prime Minister's Questions, that sacred fixture in the Commons weekly calendar, has been handed to "Hague and Harman" while Messrs Cameron, Clegg and Miliband focus on trying to save the UK and, for that matter, their jobs.

Will the arrival of the "three amigos" be portrayed as a another sign of panic? Certainly. The time for worrying about the appearance of panic, however, has passed; the more pressing concern for the pro-UK parties is to impress on voters how serious a pass the campaign has come to and the importance for all those who wish Scotland to remain in the UK, of turning out to vote. Their intention is also to maintain the momentum created by Mr Brown's speech on Monday night setting out a timetable for the delivery of greater devolution for Scotland if the nation votes No next week. Since that speech, it is Better Together that has been setting the daily agenda, even if the frenzy of activity has looked at times like a case of the heebee-geebees.

The three UK party leaders are far from being the most popular of figures here in Scotland and Yes campaigners will undoubtedly be preparing to gate crash their visit, hoping to ensure that the TV pictures that result are as counterproductive for Better Together as possible. That is politics. With Operation Save the Union now on a code red, however, the trio clearly judge that such risks must be taken. The alternative, staying away, would no doubt be portrayed by opponents as astonishing complacency.

Better Together seems belatedly to have found its passion. But has it come too late to win the day for the No camp?