A huge swing by Catholic voters away from their traditional support for Labour helped ensure the almost total wipeout of the party by the Scottish nationalists in last week’s general election.

In what had been a Labour stronghold for generations, Scotland changed colour as the Scottish National Party (SNP) took 56 of the country’s 59 Westminster seats.

An exclusive YouGov survey for The Tablet taken in the run-up to the election showed that close to half (48 per cent) of Catholics polled in Scotland said they were planning to vote for the SNP compared with 38 per cent for Labour.

Among those in Scotland who regard themselves as religious, 34 per cent said they would vote SNP, compared with 32 per cent for Labour and 22 per cent for the Conservatives.

In Britain as a whole, of the 1,260 self-identifying Catholics polled – 41 per cent said they planned to vote Labour and 31 per cent Conservative. The preference for Labour, however, appears to have waned as in 2005 an Ipsos MORI poll for The Tablet found that 53 per cent of Catholics were Labour supporters.

The YouGov poll also reveals that support for the UK Independence Party (Ukip) increased among Catholics, with 13 per cent saying they were planning to vote for the party. In 2005 support for any party other than the three main ones stood at just 6 per cent. Ukip is higher among Catholic men, at 15 per cent, than women, at 10 per cent.

Reflecting on the result in Scotland the Catholic historian, Sir Tom Devine, said the SNP has “very cunningly and effectively” stolen the left-wing ideological clothes of Labour with a plot launched decades ago.

In what he described as a deliberate tactic, the SNP targeted the Labour-dominated constituencies in western Scotland with substantial Catholic minorities.

“Back in the 1960s, the SNP was a toxic brand for Catholics, who regarded it as a Protestant party and believed that even minor devolution would simply mean a strengthening of Kirk or Protestant power,” said Sir Tom.

He explained that attitudes began to change during the Thatcher years and by the 1990s the SNP started to seek support from Catholic voters.

“They [the SNP] became very strong supporters of things like the denominational education system and courted people like Cardinal Thomas Winning [Archbishop of Glasgow from 1974 to 2001] who became quite close to Alex Salmond,” said Sir Tom. “In due course Winning actually stated that he was quite comfortable with Scottish nationalism.”

It was a view also supported by the former Archbishop of St Andrews and Edinburgh, Cardinal Keith O’Brien. Sir Tom described how at the same time the Catholic community was evolving from a disadvantaged group to mainstream Scottish society. By the 2001 census, the profile of Scotland suggested Catholicism was part of the norm.

“The old fear about sectarianism had gone and integration had taken place,” the historian suggested. “So when Catholics became mainstream, they behaved like other mainstream Scots and reacted the same way as people in other areas of the ‘Labour empire’ to the general reasons for the decline of Labour.”

Sir Tom cited as a further explanation the demographic make-up of the Catholic community. While the Kirk’s average age is more than 50 – an age group generally opposed to enhanced devolution or independence – Catholics encompass a wider age spread, including people from their twenties to early forties, which was the core group of independence supporters.