A noticeable change happened this week; the debate on Scotland's future shifted up a gear.

Whitehall sources made clear battle was now well and truly joined and we can expect to see a great deal more activity on "the Scotland front".

A few weeks back it was reported how the next stage of the pro-UK campaign was how the English voice would be used to soothe the Scottish heart.

Earlier this week, a poll showed a majority of those south of the Border did not want Scotland to leave the UK. Today, David Cameron will drape himself in red, white and blue and warn how the Union would be diminished by the loss of dear old Scotland.

Dr Johnson famously described patriotism as "the last vestige of the scoundrel". Jokingly, just a few days ago Alex Salmond inverted the aphorism, saying: "A lack of patriotism was the last vestige of the scoundrel."

But despite the Prime Minister donning his Union Jack waistcoat, the most significant development this week was the intervention of an American called Bob Dudley.

The boss of BP's call for Scotland not to "drift off" and that independence would create "big uncertainties" threw a large stone into the referendum pool. The First Minister's response was to downplay Mr Dudley's intervention as a mere personal opinion.

Then Colin Welsh from energy investment banking firm Simmons and Co popped up to say the SNP's economic argument was based on "flawed logic".

Philip Dunne, the Defence Procurement Minister, urged defence companies to air their concerns about independence "at every opportunity".

This led the SNP to launch a fightback. It accused the Ministry of Defence of trying to "pressure companies which depend on MoD orders and contracts to speak out on behalf of the No campaign".

Business for Scotland announced it now had 1324 members and released a list of chief executives who supported independence albeit just eight.

Nicola Sturgeon bristled at Mr Cameron's "cowardly" speech and accused him of a "shameful" bid to politicise the Olympics. The Deputy First Minister insisted all his speech showed was that the No camp was "rattled".

Yet one could be forgiven for thinking that it looked the other way round.