Its momentum has been gained from various political and economic crises and in large part, a feeling of alienation from Westminster.

In the early 1900s, many Scots wanted to see their thriving industrial and agricultural sectors harnessed to tackle poverty at home, especially when the Depression hit.

Although Labour was formally committed to Home Rule throughout the 1920s, over the following decade it slipped down the party's list of priorities. This was emphasised when the pro-Home Rule Independent Labour Party broke away in 1932.

The SNP won its first seat in Motherwell in 1945

Two years later, the Scottish National Party was formed through an amalgamation of the National Party of Scotland and the Scottish Party - a breakaway section of the Cathcart Conservative Association.

The party won its first seat in Motherwell in 1945, taking advantage of the war-time convention under which the Conservative, Labour and Liberal parties agreed not to contest by-elections. But the joy was short-lived.

A few months later, at the General Election, the seat was lost. The next two decades were barren for the SNP in terms of electoral success.

A Scottish Convention was formed in 1947, with the hope of securing a Parliament for Scotland along non-party lines.

Stone seized

Two years later, it drew up the Scottish Covenant, which was eventually signed by two million people. But it made little impact as all the Westminster parties still kept devolution off the main parliamentary agenda.

Winnie Ewing gave the SNP its first major success in 1967

Even when nationalists seized the Stone of Destiny from Westminster Abbey in 1950, raising the profile of its agenda, the SNP could only poll 0.3% of the Scottish vote in the 1951 General Election.

The party's first major breakthrough came in 1967 when Winnie Ewing won a by-election in the normally solidly Labour seat of Hamilton.

The victory helped to prompt a flurry of activity from Westminster, with the main parties reluctantly taking Home Rule on board.

The Conservatives, then in opposition, responded with the Declaration of Perth at their conference in 1968. This favoured a form of devolution.

Two years later, a committee chaired by former Prime Minister Sir Alec Douglas Home radically recommended a directly-elected body with legislative power.

Oil bonanza

Labour's conversion to devolution came a little later and was slightly more difficult. The Kilbrandon Royal Commission on constitutional reform reported in 1973. But its proposals for a Scottish Assembly were not greeted enthusiastically by Scottish Labour.

The discovery of North Sea oil removed many of the economic fears associated with secession. At the February General Election in 1974, the SNP polled 21.9% of the popular vote, giving it seven seats.

When the country voted again that October, the SNP attracted 30.4%, raising the number of MPs to 11.

Between the two elections, on 22 June, Labour's Scottish executive met to ratify the proposals for devolution. Unfortunately, this was also the day of the Scotland v Yugoslavia World Cup match and only 11 members turned up.

Most of those who had stayed away to watch the football were pro-devolution, giving their critics the chance to reject the plan.

In 1977, a Devolution Bill was introduced by the Callaghan government, failed. However, the SNP's good showing at the district council elections in May that year sent the message to Labour that it could not sit back and in November, a second Bill was introduced.

Included in this was the "40% rule" or the "Cunningham Amendment". This stated that if less than 40% of the electorate voted "yes" then the Scotland Act granting devolution should be repealed.