Leading article: The unique usefulness of a maverick

The Business Secretary, Vince Cable, became the most senior Liberal Democrat to share a platform with the Labour leader, when he joined Ed Miliband yesterday to call for a Yes vote in next month's referendum. It was the second unfamiliar pairing on a day which also saw David Cameron making common cause with his erstwhile arch-enemy on almost everything, the former Labour attack-dog, John (now Lord) Reid.

While a double-act with Mr Miliband was not obviously the most comfortable perch for Mr Cable – who was making his first public appearance since his caustic criticism of Mr Cameron's immigration speech last week – his contribution served to underline some of the reasons why the Business Secretary, as it often seems, leads such a charmed life. To put it at its most basic, his position as honorary maverick within the Liberal Democrats and the Coalition makes him uniquely useful.

Yesterday Mr Cable's usefulness was twofold. First, he was not Nick Clegg – whose perceived betrayal, notably over student fees, is thought by many to have made him a liability to the Yes campaign. Second, Mr Cable, who wore his agonies over tuition fees openly, berated the banks, and won concessions on visas for non-EU students and workers, is seen to have preserved something of the left – which gives him and Mr Miliband something to talk about, not just now, but perhaps in future, too.

Some of the same factors also make Mr Cable an asset to his party with elections on the horizon. While loyally defending the party's decision to join the Coalition, he is regarded as having kept the Liberal Democrat faith – which gives the party's candidates and voters a familiar point of reference. His ability to seem inside and outside the Coalition at the same time is why his periodic criticism of the Conservatives is indulged and why his reckless indiscretion to the disguised Telegraph journalists about his opposition to Rupert Murdoch, even as he was considering Murdoch's bid to control BSkyB, did not precipitate summary dismissal. Quite simply, the man who inveighed against banks too big to fail is too big an all-round asset to lose his job.