Peter Duncan is Managing Director of Message Matters, and is a former MP and Chairman of the Scottish Conservatives.

I suggested a week ago in an article for the Scottish press that there was still time for a last gasp offer from the Prime Minister to tip the balance on the independence referendum. The reaction was expectedly polarised – I was met with a combination of disbelief and derision in some quarters. That we are now, a week later, about to hear further from the unionist parties on an offer of enhanced devolution indicates how far the balance of the referendum campaign has deteriorated in the last seven days from a unionist perspective.

We are now in the end game – and unionists are being comprehensively out-fought in the run up to polling day. Those with connections into Downing Street are saying that the situation is serious, and that it is being given urgent attention.

That’s good. It’s late, very late, but its welcome.

It is worth saying, that if the referendum is lost, and Scotland votes for independence, then the name on the tombstone of the United Kingdom will be that of the Scottish Labour Party. They have been complacent to the point of neglect, and are now being defeated in the battleground that all the pundits assumed would be theirs for the taking – the large housing estates of west-central Scotland. A remarkable 30 per cent of Scottish Labour voters is now intending to vote Yes, a proportion that should humble those in Labour who now face long-term oblivion should Scotland, and its 40 or so Labour MPs at Westminster, be lost.

Labour has at no stage committed everything to the campaign, being often more interested in post-referendum positioning that pre-referendum campaigning. When what was required was a complete buy-in to Better Together, what was delivered was complexity and divisiveness through the launch of the splinter group “United with Labour”. Labour believed they could afford such game playing. They were wrong, and we are now in a dogfight to scrape a win in ten days time and hold the united Kingdom together.

But let’s leave such blame allocation for the aftermath of whatever happens.  Right now, let us do what we can to win and hold the Union together.

It is clear now that an announcement is to be made by the unionist parties – a last roll of the dice is being planned. That is welcome, because something has to change the dynamic of a growing momentum for Yes, which has arguably been rolling since the late autumn of last year. The plan sounds like a very late bid to meet the aspirations of the bulk of ordinary Scots who want a more powerful and accountable Scottish Parliament, but who do not want to leave the United Kingdom. It is a last gasp offer that is clearly targeted at the third of Labour voters, and the less important seven per cent of Conservative voters in Scotland, who are willing to vote for independence because they see it as the only route to a more empowered Parliament.

Be in no doubt: this announcement has the potential to determine the result – it could arrest the decline in No voters, or it has the potential to confirm the narrative that unionists are desperate, willing to promise anything, and in any case will never deliver the change they promise.

Put simply, George Osborne set expectations running on the Marr programme yesterday, and if the proposals for enhanced devolution that are announced do not meet those expectations, then the referendum could well be lost.

I hope lights are burning late into the night this week in Whitehall as a significant deal is patched together. Downing Street has strong cards to play to enforce some greater ambition from Labour. David Cameron and Nick Clegg could, within the existing powers granted to them by the Scotland Act of 2012, announce that income tax will be devolved immediately after a No vote. They could announce further work on the feasibility of corporation tax and VAT revenues to be assigned or devolved by the time of the last budget of this Parliament. They could seize the initiative and do it themselves.

However, it sounds as though a consensus with Labour is being sought – and that is to be welcomed. Unionists should ideally speak with one voice. However, Number 10 must play hard-ball with the Labour leadership. It is their MPs who have dragged their heels and put self-interest before winning the campaign. For a three-way agreement, Ed Miliband will have to be decisive and lead. If he is not willing to do that, then the Prime Minister has to do so, and announce immediate Coalition plans to stride forward with further devolution.

Either way, what must not happen is for the offer that will to be set out later this week to be a paltry re-packaging of previous commitments set out against a background of vague timetabling.

Many of us have been warning for months and years that action was required to avert a disaster. The poll last weekend, showing a majority of Scots willing to vote for independence, should be enough to wake most from their slumber.  A big offer now is late, indeed too late for over 650,000 postal voters who have mostly all returned their ballots already. We are in the last chance saloon – but it is not too late for something dramatic that could save the Union.