No Boris bounce for Brexit campaign as Remain pulls ahead

Boris Johnson's backing for the campaign to leave the EU has so far failed to have any significant impact on the referendum battle, with 'Remain' still ahead both in the polls and with bookmakers.

Johnson's announcement gained blanket coverage in the press at the start of the week with many commentators suggesting he had "electrified" the Leave campaign. However he was subsequently savaged by David Cameron in the Commons, with the prime minister implying Boris had only backed Brexit because of personal ambition. The latest data shows that overall he has failed to switch the fundamentals of the race.

Despite some previous polls suggesting that Johnson could be an important factor in deciding people's vote, polls released since his announcement have failed to show any significant boost for Leave. One poll, conducted by YouGov between Sunday and Tuesday this week, found support for leaving the EU had actually dropped seven points to 38% since the start of the month. The latest poll of polls puts Remain ten points ahead of Leave by 55% to 45%.

Punters were even less impressed. Perhaps surprisingly, analysis by the betting exchange 'Matchbook' actually found a bump of two per cent for 'Remain' in the betting markets following Johnson's announcement. This was on top of another eight per cent boost for 'Remain' following David Cameron's announcement of his EU deal at the weekend.

Overall, bookies estimate the implied probability of the UK staying in the EU at around 72%, up several points from the start of the week.

Pollsters are continuing to find a big difference between polls conducted by phone and those conducted online, with the latter finding much more support for Brexit.

However, polling experts say that the underlying data heavily favours Remain.

One pollster, which found a one-point lead for Leave this week, released an editorial explaining why the fundamentals still overwhelmingly favour the campaign to stay in the EU.

YouGov released data showing that voters currently believe Brexit will damage Britain's economy, cost jobs and harm our influence in the world. They also found evidence that the Remain vote has greater potential to win over undecided voters than the Leave campaign.

Many commentators have questioned Boris's motivation for backing Brexit despite previously telling friends that he is 'not an Outer'. Others have questioned exactly how hard he will campaign in its favour given his commitment not to debate other Conservative politicians on the issue.

Boris's enthusiasm may depend on how winnable he believes it is. One City Hall source tells me they overheard the London mayor this week jokingly describing the Brexit campaign as a lost cause. The evidence from pollsters and bookies this week suggests he could be right.