Alex Salmond's nationalism was nurtured as a child on his grand-father's knee, being told stories from Scottish history.

Yesterday, the SNP leader made history himself, naming the date when Scots will vote in a referendum on independence.

The First Minister carved another milestone in his political career when he told a packed Holyrood chamber: "I'm honoured that on Thursday, September 18, 2014, we will hold Scotland's referendum – a historic day when the people will decide Scotland's future.

"I believe it will be the day we take responsibility for our country."

In unveiling the Scottish Independence Referendum Bill he started the clock ticking on the biggest decision the country has faced in 300 years.

It was a momentous occasion for Mr Salmond, who has campaigned his whole life to bring the country to a decision, and his party, which has striven for more three-quarters of a century. For most of those years they had little prospect of success.

Mr Salmond insisted the bill was "the most important legislation to have been introduced since the Scottish Parliament was reconvened".

The legislation runs to 146 pages but few, aside from campaign strategists or election officials, will bother with the last 145.

Section 1, Clause 1 states: "A referendum is to be held in Scotland on a question about the independence of Scotland."

The date is spelled out a few paragraphs later. In a political world full of "worst kept secrets" the date really was the best kept secret. Bins near ministers' offices were rummaged on Tuesday night, it has been alleged, but nothing was found.

Only a handful of insiders was in the tightest of loops. The date was not discussed at Tuesday's cabinet meeting and most ministers had to wait, like everyone else, to hear it announced in Parliament.

There was an all-too-rare sense of theatre about the place. The announcement was greeted with huge excitement among Nationalist MSPs who shared their delight on Twitter.

The pro-independence Yes group arranged for campaigners to hold up placards displaying the date at sites around the country.

After his statement, the First Minister strolled with Nicola Sturgeon, his deputy, to a grassy bank outside the parliament building where, for the benefit of photographers, the date was spelled out in 3ft-high letters.

In a bid to take the wind out of his sails, Labour MSP James Kelly remarked: "This was the day Alex Salmond put his retirement date in statute."

It was a good line but dampening the Nationalist mood was a forlorn hope.

The announcement was timed to propel the SNP faithful towards their conference in Inverness this weekend fighting fit.

Mr Salmond will address them on Saturday afternoon and will surely brandish the bill when he rallies his troops. They will leave knowing the campaign proper has begun.

The First Minister has stuck to his plan – devised in the final days of the last election, when the SNP knew it was on course for a crushing victory – to hold the referendum in the autumn of 2014.

September 18 is earlier than expected.

By plumping for it, the Government has ensured the campaign will enter its final weeks in the afterglow of the Glasgow Commonwealth Games, when Mr Salmond hopes the sight of athletes competing and winning for Scotland, rather than Team GB, will boost support for independence.

The date avoids the Ryder Cup golf tournament at Gleneagles later in the month and, more importantly, any potential criticism from the Electoral Commission.

The independent elections watchdog – confirmed in the bill as the referendum referee – is due to report on progress within the next few months. It may have questioned holding the poll on a Saturday – as one paper previously revealed – during school holidays or into the shorter days and darker nights of late October or November.

Johann Lamont, the Scottish Labour leader, criticised the long delay until the vote, claiming Scotland would remain "on pause" for the next 18 months.

She said the Yes camp would have been "routed" had the vote been held now.

The latest opinion polls show support for independence trailing by around 20 points. But, as of yesterday, all those campaigning for a Yes vote know exactly how much time they have to turn the tide.