The Unionist Party, referred to as the Scottish Unionist Party outwith Scotland itself, was the main centre right political party in Scotland between 1912 and 1965. Use of the terms 'Tory', and 'Unionist', as opposed to 'Conservative', is a consequence of the Scottish Unionists eschewing the name 'Conservative' [1] until 1965.
Independent of, though associated with, the Conservative Party in England and Wales, it stood for election at different periods of its history in alliance with a small number of Liberal Unionist and National Liberal candidates. Those who successfully became Members of Parliament (MPs) would then take the Conservative Whip at Westminster just as the Ulster Unionists did until 1973, or as current Conservative Member of the European Parliament (MEPs) do within the European People's Party in the European Parliament. At Westminster the differences between the Scottish Unionist and the English (and Welsh) party could appear blurred or non-existent to the external casual observer, especially as many Scottish MPs were prominent in the parliamentary Conservative party, such as party leaders Andrew Bonar Law (1911-1921 & 1922-1923) and Sir Alec Douglas-Home (1963-1965), both of whom served as Prime Minister of the United Kingdom.
The party traditionally did not stand at local government level but instead supported and assisted the Progressive Party in its campaigns against the British Labour Party. This relationship ended when the Conservatives started fielding their own candidates, who stood against both Labour and the Progressives.

Ethos and appeal
Compared to the UK Conservative Party's pre-1886 record in Scotland, as well as the post-1965 Scottish Conservative and Unionist Party, the 1912-1965 Scottish Unionist Party's electoral record stands out as a success.
With the UK Liberal Party divided and declining, the Scottish Unionist Party managed to attract former Liberal voters during this period — sometimes with candidates standing on a Liberal Unionist ticket. The creation of the National Liberals also assisted the Unionist vote.
Within this context their support grew, and the emergence of the Labour party as a threat to the middle-classes resulted in the Scottish Unionists achieving a majority of Scottish seats in the 1924 election, 37 out of Scotland's 73. Suffering a setback in 1929, they reasserted themselves in the 1931 election during an electoral backlash against the Labour Party that resulted in the creation of the National Government. The Scottish Unionist Party won 79% of the Scottish seats that year: 58 out of 73. The following election of 1935 returned a reduced majority of 45 MPs.
This remained the situation until Labour's landslide victory in the 1945 election. The Unionists won only 30 of the (now) 71 constituencies. In the 1950 election, a majority of Labour MPs was returned again, but the Scottish Unionist Party closed the gap by returning 32 MPs. The Conservatives had suffered devastating losses in England & Wales between 1945 and 1950, and the addition of the Scottish Unionist MPs proved vital. In the subsequent Conservative election victory of 1951, an equal number of Labour and Unionist MPs were returned from Scotland, 35, with one solitary Liberal taking the remaining seat.
With Church of Scotland membership reaching record levels, the 1955 election brought unparalleled success as the party gained 50.1% of the vote and 36 of the 71 seats at Westminster. Often cited as the only party to achieve a majority of the Scottish vote, it should be pointed out that 6 of the Conservative and Unionist MPs were returned that year under the label of 'Liberal Unionist' or 'National Liberal'. And this apparent success was the prelude to a number of events that weakened the appeal of the both the Scottish Unionist Party and the Scottish Conservative branch that followed.

Electoral record and the 1955 election
Only a year after the 1955 triumph, one event signaled the unraveling of the thread that had until then united Scottish Unionist support: the humiliation of the 1956 Suez Crisis. The event was a symbolic end for the British Empire; not only was British power seen to be eclipsed by the United States, but the unity of the Empire itself came into question. It was at this time that Canada's Lester Pearson led the United Nations' calls for a negotiated settlement and even offered Canadian troops as neutral peacekeepers to replace British soldiers.
Furthermore, in 1960 Conservative Prime Minister Harold Macmillan made his "Winds of Change" speech to the South African Parliament. This signaled an end to the colonial administration of British Empire overseas possessions and began their emergence as independent states. The change in Conservative attitudes to the cohesion of the British Empire had been illustrated earlier in 1958 with the expulsion of the League of Empire Loyalists from the Conservative Party Conference.
Psychologically these events marked the end of the British Empire, and with it the central thread of popular imperial unity which had bolstered the Scottish Unionist Party until then. In the 1959 election that saw the Unionist's sister Conservative party increase their overall majority in the Commons, the Scottish Unionist's own vote declined, and four MPs lost their seats. In the Conservative defeat of 1964 eight more Unionist MPs were lost.

Merger with the UK Conservative Party
As the British Empire came to an end, so to did the primacy of Protestant associations, as secularism and ecumenicalism rose. The decline of strictly Protestant associations, and the loss of it Protestant working-class base, spelled the erosion of the Unionist vote. Though many Conservatives would still identify with the Kirk, most members of the established Church of Scotland did not identify themselves as Conservatives.
With the Daily Record newspaper switching from the Unionists to Labour, the UK Conservative Party in the 1960s was mercilessly portrayed as a party of the Anglicised aristocracy. Combined with the new name, this helped switch previous Unionist voters to the Labour party and the SNP, which advanced considerably in the elections of February and October 1974.
The relations between the Scottish Conservatives with the largely working-class Orange Order also became problematic because of the perceived aristocratic connection of the former, but it was the Troubles in Northern Ireland that created more concrete problems. On one level, there was the residual perception of a connection that many mainstream Protestant voters associated with the sectarian violence in Northern Ireland — a perception that is unfair to a large extent since the Scottish Orange Order has dealt more stringently with members associating with Northern Irish paramilitaries than its Irish equivalent. However, the ramifications of this perception also led to the Scottish Conservative Party downplaying and ignoring past associations, which further widened the gap with the Orange Order. Any links that lingered were ultimately broken when Margaret Thatcher signed the Anglo-Irish Agreement. This event witnessed the Orange Lodge (amongst other supporters) settting up its own Scottish Unionist Party.