The defence of Mr Cameron's level of involvement in trying to maintain the Union comes as he is expected to take a more hands-on approach soon with the UK Cabinet due to hold its first full meeting in Scotland before Christmas.
This has raised speculation the PM may, for impact, cross the Border just days before the First Minister launches his eagerly-awaited White Paper on independence. Mr Salmond is due to do so in November.
Coalition sources have made clear that Mr Cameron needs at some stage soon to take on a higher profile in the independence debate. "He is, after all, the Prime Minister of Scotland," said one UK Government insider.
No 10 said while the PM was a passionate defender of the UK, the debate was "primarily" for Scottish voices even though it pointed to Whitehall's leading role in producing analysis papers on Scottish independence.
Asked if the PM was intent to take a back seat in the campaign, his spokesman, stressing how Mr Cameron had made a number of visits to Scotland - the most recent only last week - replied: "I would disagree he is taking a back seat. He has been making his view on this very clear. He has been making it and continues to make it."
An SNP spokesman said the Downing Street remarks confirmed "the Tories are pulling the strings of the anti-independence campaign, despite having been consistently and overwhelmingly rejected by people in Scotland".
He added: "The Prime Minister has so far refused the invitation to debate with the First Minister but as we move towards the vote Mr Cameron will have to say why he thinks the Tories know best for Scotland."