There’s an air of inevitability about the publication of a letter from business leaders warning against a Labour government in today’s Daily Telegraph.

The Tories can always count on a swathe of blue chip executives to back their cause. (Presumably self-interest plays a part too, as the signatories are classic targets of Labour’s 50p top rate and the mansion tax).

There is is no argument that letters like this work. They are simple to put together, get broadcast follow-up and help frame the day’s coverage. They matter because the grand fromages of the business world represent an important barometer of credibility for any party.

Yet as a tactic, the business leader round-robin was more counter-intuitive – and seemed more effective – when Labour did it in previous elections.

And the timing of today’s letter feels like a reactive move by the Tories – as though party strategists had this pencilled-in for later in the campaign.

To have real purchase, publishing a list of business endorsers nearer to polling day would surely be more effective; showing momentum behind the Tory campaign and contrasting that with Labour’s failure to convince business about its fitness to govern.

Throwing it in during the first week feels like the waste of a valuable asset. Like when contestants on ‘Who Wants to be a Millionaire?’ phone a friend on one of the easy questions.

As ever in politics, when someone does something unexpected, it’s because they are rattled.

Could it be that Labour’s efforts this week to burnish their business credentials, contrasting the Tories’ pledge of an in/out referendum on the EU with Labour’s solid, if unfashionable, pro-European-ness, have spooked Tory high command?

After all, this is one of the few areas where the Tories “competence versus chaos” line reverses in Labour’s favour.

As David Cameron limbers up for the seven-way leaders’ debate, (after his uncertain performance against Paxman) he needs to project calm, statesmanlike competence. To show that he is a safe bet.

Does he need to wheel out his pin-striped pals this early in the campaign to get that message across?

Perhaps he does.