There was also surprise that there are no plans for either Cameron or senior Tory ministers to hit the campaign trail in Scotland this week despite the enormity of what is at stake.
Cameron is under pressure to ask the Queen to speak out in support of the union. Senior MPs have suggested an intervention from Her Majesty could "make all the difference". She did in 1977 when Scotland and Wales were voting on devolved national assemblies. She said she understood "aspirations" of devolved power but: "I cannot forget that I was crowned Queen of the United Kingdom of Great Britain and of Northern Ireland. Perhaps this Jubilee is a time to remind ourselves of the benefits which union has conferred, at home and in our international dealings, on the inhabitants of all parts of the United Kingdom."
The choice of the former Prime Minister to detail the devolution plans is also a rebuff for Alistair Darling, the head of Better Together, who was mauled by Alex Salmond in a televised debate last month.
The uncertainty over the referendum result sent the pound plunging and wiped billions off the stock market value of major Scottish firms.
In Midlothian, Brown disclosed his timetable for the implementation of a "modern form of Scottish Home Rule" following a No vote. It is also being backed by the Conservative and Liberal Democrat parties.
Under the plan, details of fresh devolution of tax and welfare powers would be agreed by late November and legislation drafted next January.
Brown said: "A No vote on September 18 will not be an end point, but the starting gun for action on September 19, when straight away we will kick off a plan to deliver the enhanced devolution that we want."
Yes Scotland reacted to Brown's move with contempt, claiming it was fresh evidence of the "utter panic and desperation" within the No camp.
The discontent in the No camp emerged as the second opinion poll in 48 hours showed it is losing ground while the Yes campaign is gaining support, meaning there is now nothing to divide the two sides.
A survey by TNS found 41 per cent of people who said they would definitely vote were in favour of independence with the same proportion in favour of staying in the UK. This represents a 3 per cent gain for the Yes campaign and a 5 per cent loss for the No side in a month. When "don't knows" are excluded, the two sides are locked on 50 per cent each.
The research shows 600,000 voters may not have made up their minds, with 18 per cent saying they were undecided but intended to vote.
- Telegraph Group Ltd
