The head of the anti-independence campaign in Scotland, Labour's Alistair Darling, has allegedly been accused of being "dreary and comatose" by senior Tories.

In what appears to be a campaign to rubbish the former chancellor, it has been reported that one source claimed: "The man has never run a campaign. He is comatose most of the time" adding that he was a "dreary figurehead".

The whispering campaign is said to reflect a view in Downing Street, flatly denied, that the "Yes" to independence campaign and its leader Alex Salmond are making all the running in the referendum battle which will end in an historic vote in 10 months time.

Prime Minister David Cameron recently sacked his Scottish Secretary Michael Moore, allegedly because he was not seen as robust enough in challenging Salmond, and replaced him with Alistair Carmichael.

Now it is the head of the "Better Together" campaign, Darling, who appears to be under fire.

But this is a hugely risky move. For a start, it suggests the Tories fear the "No" campaign is failing - despite repeated polls suggesting there is still the overwhelming likelihood of a no vote in the referendum.

The trouble is, David Cameron knows the more he and his own team attempt to pitch into the campaign the more they are likely to drive voters, particularly the 17% or so of undecideds, into the "Yes" camp.

Secondly it misses the point of Alistair Darling. As his record in government proved time and again, he has always used his solid, un-exciting persona to steer steady, safe, uncontroversial ways through difficult waters. That was one of the reasons he was chosen for the job in the first place.

The great fear was always that any leader who was too aggressive would run the risk of alienating voters, particularly if there was any suggestion they were the Tory party's favoured candidate.

Suggestions that the Tories would secretly like the see Scotland separated because that would ensure them a permanent parliamentary majority in the rest of the country have also been dismissed on the grounds there is simply no sensible evidence to support the case.

It is no surprise, then, that Downing Street are flatly denying the reports. The prime minister's spokesman said: "We have the very highest regard for the way he is doing it. I can emphatically tell you that the Prime Minister thinks Alistair Darling is absolutely the right person."

They would, of course, say that. But Cameron and his team are hugely aware of the dangers any public squabbling in the "Better Together" campaign would pose.

For a start it would instantly be re-branded the "Better Apart" campaign by the SNP.