COALITION Ministers are considering drawing up a "Black Paper" over the summer to set out the key questions they believe Alex Salmond's much-awaited White Paper on Scottish independence must answer.

"We have to emphasise to the public the big black holes that currently exist in the Scottish Government's prospectus and make clear the First Minister needs to answer major questions if his case is to have a shred of credibility; at the moment, it clearly doesn't," said one Whitehall insider.

Salmond's White Paper is due in November.

Last week, George Osborne expressed astonishment that the Nationalist case for independence was "very thin". While stressing the Coalition was far from complacent, the Chancellor insisted much progress had been made in articulating the pro-UK cause.

"The Unionist case is far stronger and better articulated than it was two years ago because we called the SNP's bluff and said let's have the referendum and challenged them to make the arguments for independence."

Mr Osborne added: "Those arguments are turning out to be very thin and they can't answer the most basic questions about the issue of currency."

Earlier this month, Prime Minister David Cameron boasted the UK Government was "winning all the arguments" while a senior Coalition source went further to claim the referendum campaign had been already won with 14 months to go to polling day.

The SNP hit back, insisting the Coalition was taking Scottish votes for granted and that claims of a Unionist victory "reeked of typical Tory arrogance".

Last month, Alex Salmond described the campaign thus far as "the phoney war" and indicated that, while the Yes Campaign was lagging behind in the polls, much ground could be made up.

"This is not the campaign," he declared. "I went into an election in 2011 20 points behind in the polls and ended up 15 in front. The real game hasn't even started. We are just clearing the ground."

Already, the Coalition has published four of 13 expected analysis papers, covering the legal status of the UK, the currency, the financial sector and the micro-economy such postal services. Others will cover international matters such as EU membership, energy, including North Sea oil and gas, defence and welfare. The next one is expected in September, possibly to coincide with the year-to-go milestone.