Ferry operator Caledonian MacBrayne angered local Christians when it began its first Sunday crossing from the Scottish mainland to Stornoway on the staunchly Christian Isle of Lewis in July.

The service, which runs every Sunday at 2.30pm, was launched after more than 20 years of fierce campaigning by local churches to keep the Sabbath as a day of rest.

While the ferry operator said it would be breaking European laws if it did not run the service, local Christians said they feared it would lead to the secularisation of their island.

In a letter to the Stornoway Gazette, the Rev George Hargreaves said the service was “a cultural wrecking ball that will, if allowed to continue, destroy the Western Isles’ unique selling point – its distinctive culture”.

The Scottish Christian Party remains the third largest party in the Western Isles after polling nine per cent of the vote in the recent elections to the European Parliament.

Rev Hargreaves admitted it had been a mistake to give the SNP and Labour a clear run in the Western Isles constituency in the 2007 Scottish Parliament election.

“Not standing in the Western Isles in 2007 has proved to be a tactical disaster,” he wrote. “At the time it meant that our lead regional candidate, Murdo Murray – a local Western Islander – was sidelined at the local hustings, and the opinion pollsters ignored our local support because we did not ‘officially’ have a local candidate.”

Rev Hargreaves said the Scottish Christian Party planned to run election campaigns in 2010 and 2011 based on “building the strengths of the Western Isles, not destroying them”.

“We intend to see the people of the Western Isles united behind it uniqueness, not divided by its diversity,” he said.

“As for the Sunday ferry services to the Western Isles, we shall use the electoral process to see it stopped.

“After all, the SNP can hardly afford to lose MPs and MSPs over the matter.”