Is Vince Cable as popular as polls suggest?

As the results of today's Cabinet reshuffle were absorbed around Westminster, some Liberal Democrat malcontents have been speculating about a reshuffle at the top of their own party, with Business Secretary Vince Cable often touted as a popular replacement for current leader Nick Clegg.

So with the Lib Dem conference little over a fortnight away, Mr Clegg's camp might have been alarmed this morning by two polls which purported to show that Mr Cable would prove a more popular choice with the electorate.

In fact, the Independent - which commissioned one of the polls from ComRes - claimed that the results showed that:

"The Liberal Democrats would win almost twice as many seats at the next election under Vince Cable as they would under Nick Clegg."

Similarly, YouGov research for the Sun suggested that the party would benefit from a boost of three percentage points should the Business Secretary dethrone the party leader.

While polls which test the popularity of a pretender to a particular party's top job are not uncommon (recent polls have also looked at Boris Johnson's prospects should he take the Conservative Leadership) and ask perfectly legitimate questions, we do need to be careful about the degree of certainty that can be attached to the results.

As polling expert Anthony Wells has repeatedly shown over at UK Polling Report, hypothetical questions such as these are speculative in their nature and it can be hard to judge how far the results mirror genuine public enthusiasm for a change in leadership.

In particular, we should bear in mind that we don't know what Mr Cable would do differently were he Lib Dem leader, and wavering supporters of the party may be projecting their own hopes and desires for the party onto a hypothetical Cable premiership. Whether or not these would be fulfilled in the event that Mr Cable takes the reins is uncertain, so we don't know if the party could expect the extra support suggested by the polls at the time of a general election.

In spite of this uncertainty, we can look to a concrete example in Gordon Brown, whose protracted bid to take the Labour party leadership prompted many polls about his popularity with the electorate as prospective PM before he entered Downing Street.

As we can see from the chart below, polls generally predicted that Labour would prove less popular with voters under a Brown premiership than it would under Tony Blair before the former eventually succeeded the latter in the summer of 2007. However immediately following this transition, the polls suggested that Labour's support had increased as a result of the change.

This isn't necessarily inconsistent: as Mr Wells pointed out at the time, the increased media focus on Gordon Brown personally coupled with the novelty of his policies (which hadn't had a chance to either succeed or fail) may have meant more people were willing to give him a chance once his elevation to Number 10 was confirmed.

In the longer term, the polling bounce wasn't sustained, although we can only speculate as to whether Labour would have performed better at the general election had Mr Blair remained party leader.

So while today's polls are interesting as a snapshot of the relative popularity of Mr Clegg and Mr Cable at the moment, it is a stretch to say with any certainty that this would necessarily translate to double the number of seats for the Lib Dems at the next election.