BRITAIN'S coalition government was under pressure last night after its business secretary was stripped of key powers following his remark that he had ''declared war'' on media mogul Rupert Murdoch.

Conservative Prime Minister David Cameron told Liberal Democrat Business Secretary Vince Cable he would no longer have a say in Mr Murdoch's bid to take full control of pay TV giant BSkyB.

Britain's Business Secretary Vince Cable arrives at the Treasury in London. Credit:Reuters

This came after Mr Cable told undercover newspaper reporters he planned to block the £7.8 billion ($A12.1 billion) bid by Mr Murdoch's News Corporation for BSkyB.

''You may wonder what is happening with the Murdoch press,'' Mr Cable told the reporters from The Daily Telegraph, posing as constituents. ''I have declared war on Mr Murdoch and I think we're going to win.''