Forget the hype. Boris Johnson will not swing the EU referendum campaign

According to the press, Boris Johnson has "electrified" the EU referendum campaign, with his backing for Leave a "major boost" to the campaign.

The smothering consensus plastered across today's newspapers is that Boris's endorsement is a massive plus for the Out campaign. But is this consensus right? Will millions of voters sitting in Yorkshire and Glasgow, Cardiff and Bristol, suddenly decide to support leaving the EU simply because the mayor of London tells them to? It seems rather unlikely to me, but let's look at the evidence.

All of the commentary on this refers to just one poll last week which asked voters to choose between a list of politicians and answer which would "be important to you in deciding how to vote in the referendum on European Union membership?" Respondents were allowed to choose as many politicians from the list as they liked.

The prime minister was the most picked in the poll, with 44% of respondents saying his voice is "important" to their choice. However, Boris came second with 32%. This fact has since been used to imply that the mayor of London could lead a third of the electorate, some 15 million people, to switch their vote in the referendum. This in turn has been used to justify Boris's presence on every single newspaper front page this morning.

But if you look further down the same poll, you see that Boris is only viewed as a narrowly more "important" voice than several other leading UK politicians. Both the home secretary Theresa May and the chancellor George Osborne were picked by 28% of respondents, almost within the margin of error of Boris, while Jeremy Corbyn was picked by 27%. Yet nobody is talking about May or Corbyn's ability to "swing" the referendum campaign.

And if the 'Boris effect' is such a positive motivating force for voters, then why hasn't it been seen in London? At the last London mayoral election more than 60% of voters didn't even bother to vote, while at the last general election (where Boris's popularity was also talked about as a major factor) the Conservatives lost seven seats to Labour in London. Even in his own back yard, Boris's impact on voters is overstated. After eight years in City Hall, most Londoners still tell pollsters they have little or no idea what the mayor of London actually does, while a City Hall survey a few years back found that one-in-five Londoners don't even know who he is. If London voters are hanging on Boris's every word then they are keeping very quiet about it.

But even if you still somehow believe that he will have a massive impact on the referendum result, it seems difficult to believe that impact will be wholly positive.

For a start, it is already abundantly clear that Boris's decision was taken almost exclusively for his own political benefit. Unlike his aspiring successor Zac Goldsmith, whose endorsement for Leave was obviously a principled one which will make it harder for him to win power, Boris's decision is a nakedly obvious attempt to increase his chances of becoming Conservative leader and prime minister.

This fact is so clear it hardly even needs stating. In neither the eight years that Boris has been mayor nor in any of the years preceding it, has he ever publicly declared a desire to leave the EU. Many of those who know him personally say he has always been broadly in favour of remaining in the union. He only told the prime minister of his change of heart within minutes of announcing it on television.

The fact that Boris is very far from an enthusiastic supporter for leaving the EU can be seen clearly in his Daily Telegraph column today which is as convoluted and equivocating an argument for exit as it is possible to imagine. As others have already commented, it reads more like an argument for further renegotiation and deliberation than it does for actually leaving the EU. If Boris has secretly been a convinced Outer all along, then it is a conviction which he continues to hide even from himself.

Now we shouldn't completely downplay the impact of Boris's endorsement. By backing Leave, Boris has made it much more likely he will one day become the next Tory leader and prime minister. For this reason alone, his announcement yesterday is big political news.

But the result of the referendum campaign will not be swung by Boris or any other leading politician. And the Leave campaign are lucky that it won't. If the leading figures on your campaign include George Galloway and Nigel Farage, then it may be time to downplay the importance of personality to the outcome.

The truth is that the referendum campaign will not be decided on personality, it will be decided on the issues. If voters decide to leave the EU it will be because they are convinced that it is a risk worth taking, it won't be because Boris has suddenly decided that supporting exit is the best chance yet of furthering his own political career.