Alex Salmond's disclosure of when he wants to hold the referendum was unexpected but his preferred date was less so

So Alex Salmond has named the day he wants to see Scotland vote for divorce; well, if not the day, then the season. The referendum on Scottish independence will be staged in autumn 2014, he suddenly declared on Tuesday night.

His announcement, while long-awaited, was still unexpectedly sudden. Many suspect the disclosure was forced on the first minister. Salmond was desperate to check-mate David Cameron's government in London, just as it warned in the Commons that a Holyrood-run referendum would be illegal without explicit powers from Westminster.

Why autumn 2014? Salmond insists it is the date which allows all sides the time to deliver the strongest campaigns, both for and against. As Wednesday's splash headline in the Scotsman loosely has it, this means "1,000 days to decide our future".

But 2014 has been very deliberately chosen: it is a year with considerable significance and resonance. Scotland will be the focus of several major global sporting and cultural events, including the Commonwealth games in Glasgow, the Ryder cup at Gleneagles and – an event with particular resonance for nationalists – the second "Year of Homecoming", a lengthy festival of Scottish cultural and artistic history.

And, of particular resonance for hardline nationalists, 2014 is also the 700th anniversary of the Battle of Bannockburn on 24 June 1314, when Robert the Bruce vanquished an English army led by Edward II; it was the decisive battle in the "first war of independence".

As the ecstatic reaction in many Scottish cinemas to Braveheart, Mel Gibson's testosterone-charged epic about Bruce's predecessor, William Wallace, showed, many Scots – men in particular – relish the idea of the heroic nation battling against an arrogant enemy.

That date will help embolden many nationalist activists, but the marketing-savvy Scottish National party knows Bannockburn is actually a very difficult date: it is potentially toxic to their claim that Salmond's Scotland is an all-embracing country, open to all regardless of ethnicity, including the English.

It also leaves the SNP mired in accusations that it is a party polluted by centuries-old grievances and romantic mythology.

Hence the mischievous suggestion peddled by anti-nationalists such as the Tory peer and arch-Thatcherite ex Scottish secretary, Michael Forsyth, that Salmond wanted to hold the referendum on that anniversary.

But Salmond wants to build up the idea that Scotland's divorce from England will be gentle and conciliatory; that Scotland wants to remain close friends and remain part of the British family. Some SNP strategists even suggest Scotland and England might continue to share services, such as embassies overseas and military bases.

That's why he reacted so vigorously to dismiss Forsyth's claim on Tuesday, as "stuff and nonsense".

Yet Salmond himself is partly to blame. In May 2010, when he confirmed that the Scottish government would stage a "Year of Homecoming" in 2014, he explicitly linked it to Bannockburn. He had no idea then he would have a landslide election victory last May, giving him the majority to deliver a referendum in the same year.

So the SNP will focus deliberately on the much more positive, optimistic and all-inclusive messages built into 2014's sports and cultural events. The homecoming festival will be a pageant of Scottishness, and is likely to feature another great clan "gathering" for the vast and vocal Scottish diaspora, which features a mass "clan march" through the Old Town of Edinburgh.

The Gathering 2009 – a two-day event celebrating Scottish culture – was a financial disaster, and less popular than its organisers hoped; but the homecoming festival in the same year, tied then to the 250th anniversary of the birth of Rabbie Burns, in all brought in 95,000 extra visitors to Scotland, generated £150m worth of publicity and saw 300 cultural and arts events held around Scotland.

And from 23 July to 4 August, Glasgow will host the 2014 Commonwealth games, when 53 nationalities will crowd into the city, a multiethnic extravaganza Salmond is certain to exploit. In September, Scotland's greatest sporting export – golf – will be celebrated at the Ryder cup contest between the USA and Europe at Gleneagles, another icon of Scottish tourism.

Tied in with both events are major campaigns engineered by the tourism agency VisitScotland, which has a marketing onslaught already underway, and the arts agency Creative Scotland, which is running a multimillion pound three-year long "year of creative Scotland" to tie in the 2012 London Olympics to the 2014 Commonwealth games.

All this may help explain why Cameron was extremely keen to press Salmond into choosing 2013 for the referendum. Apparently, not much is happening that year.

3pm update:

The Scottish government has pointed out that the "Year of Culture Scotland" title only refers to 2012, and is the launchpad for the three-year culture campaign linking this year with the Commonwealth games in 2014. The new campaign was launched today.