I've argued he can't, but John Sides flags research (pdf) suggesting otherwise:
[W]e exploit a rare change in communication flows—the endorsement switch to the Labour Party by several prominent British newspapers before the 1997 United Kingdom general election—to study the persuasive power of the news media … By comparing readers of newspapers that switched endorsements to similar individuals who did not read these newspapers, we estimate that these papers persuaded a considerable share of their readers to vote for Labour. Depending on the statistical approach, the point estimates vary from about 10% to as high as 25% of readers.
I'm not sure how you can prove causation here – especially in an election where the incumbent party had been in power for eighteen straight years – but I haven't had time to study the paper. But the idea that Labour's simply massive and unprecedented 1997 majority was dependent on Murdoch strikes me as silly on its face. British polling expert Anthony King called the epochal election "an asteroid hitting the planet and destroying practically all life on Earth". Murdoch had power, but this was Blair's victory, not his.
The Dish 