SCOTLAND faces a stark and simple choice between opportunity and inertia when it votes in the independence referendum, Alex Salmond will claim this week, as the most important political fight in the UK since the Irish war of independence finally gets under way.

In the key theme of the SNP conference, Salmond will warn that a No vote in 2014 would not be a safe or neutral option, but would consign the country to years of powerlessness and stagnation.

He will argue that rather than offering continuity or acting as a springboard to greater devolution, a No vote would leave Westminster feeling it could ignore the public's appetite for more powers and ride roughshod over Holyrood, cutting budgets and imposing unpopular policies.

Labour, the LibDems and Tories have all signalled a willingness to look at enhanced devolution for Holyrood after a No vote, including more local control over tax and spending.

Under the new Scotland Act, Holyrood is already due to gain control over income tax, stamp duty, landfill tax and borrowing from 2015.

But at this week's SNP conference in Perth, Salmond will argue any hope of further powers or flexibility would evaporate if Scotland rejected independence, as happened under the Tories when a Scottish Assembly was rejected in 1979.

The message is aimed at those who see a No vote as the automatic safe choice, and forms the "stick" in a classic carrot-and-stick strategy, in which the carrot is the SNP's promise of Scotland flourishing under independence.

Salmond and David Cameron will tomorrow fire the starting pistol on a gruelling 100-week campaign when they sign a deal on the mechanics of the referendum in a meeting on Edinburgh's Calton Hill, the scene of decades of protests demanding Scottish self-government.

The memorandum of understanding, which paves the way for a binding referendum drafted in Holyrood, marks the start of the campaign proper after a year of consultations and wrangling.

Salmond has secured most of his wish-list: control over the timing of the ballot, votes for 16 and 17-year-olds, and a legally watertight process that cannot be derailed by court challenges or end in a disputed result.

Cameron's prize is a single question on independence, rather than a two-question ballot giving Salmond a fallback option of extra powers for Holyrood.

Westminster will now pass a Section 30 Order under the 1998 Scotland Act devolving the power to run the referendum, with a sunset clause ensuring it is held by the end of 2014.

The UK Electoral Commission will oversee the campaign and police spending and donations.

With the rules settled, the focus now shifts to the substance of the independence debate, as arguments over process are replaced by deeper questions about policies and power.

"Scotland needs a Yes vote in 2014, because the consequences of a No vote are negative and stark," a senior SNP MSP told the Sunday Herald.

"Scotland would lose any political muscle we ever had with Whitehall because of the possibility of independence – take that away and you would have a situation where there was no sanction against the Treasury cutting Scotland's share of spending, we would have a new generation of Trident nuclear weapons dumped on the Clyde, and no Scottish concern, no matter how valid, would be taken seriously by Westminster.

"You don't need a crystal ball, you only have to look at the record of what happened after 1979. A Tory government trampled all over Scotland, and a Labour opposition let them do it.

"Whoever was in government at Westminster, the dynamic would be exactly the same: Scotland would have no clout so the idea of new powers coming to the parliament in that scenario is fanciful."

A TNS-BRMB poll last week found 53% of Scots would vote No tomorrow against 28% Yes, with the gap widening from 11 to 25 points this year.

But the SNP believes summer 2012 has been the "high water mark for the No campaign" because the Olympics and the Queen's Diamond Jubilee fuelled affection for Britishness and the Union. The party believes the next two years, which are likely to include two grim George Osborne budgets, will alter that perspective.

However, the centenary of the First World War in 2014, with £50m of events marking the nation's shared sacrifices through the year, may see a further surge in pro-British sentiment.

Tomorrow's ceremony follows weeks of detailed talks between LibDem Scottish Secretary Michael Moore and Deputy First Minister Nicola Sturgeon.