Academics and media commentators said that The Sun’s decision to end 12 years of support for the Labour party within hours of the keynote speech by Gordon Brown, the prime minister, on Tuesday showed that Rupert Murdoch’s tabloid paper was following its readers rather than leading them.

Employees at News International, the paper’s parent company, told the Financial Times that The Sun’s attack was aimed at the Labour party rather than personally at Mr Brown. The paper’s guarded endorsement of David Cameron reflected Mr Murdoch’s ambivalent attitude to the Conservative leadership, they said.