Almost before Boris Johnson had finished his speech on Wednesday and confirmed his desire to enter parliament, Ukip’s website had been updated. Ukip’s rising star and now deputy chairman, Suzanne Evans, declared Johnson was “selling a myth to the British people”. She continued: “How hollow and disingenuous to spend half an hour criticising Brussels, employing all the wit and wisdom possible, to conclude that campaigning to stay in is actually the best option.”

The message from Ukip high command to its voters was short but direct: real Eurosceptics are those who want to pull Britain out of the EU. By calling for reform while wanting Britain to stay in, Johnson is a fake. Do not trust him.

Ukip’s quick attempt to cover its Eurosceptic flank and respond to Boris-mania is understandable. Johnson has long been hailed as the Conservative party’s panacea; the charismatic populist who will finally silence Nigel Farage, win over Ukip voters and – for the first time since 1992 – lead the Conservatives back into real majority government.

With his natural ability to connect with ordinary voters; seem at ease with the pace and diversity of modern Britain that is nowhere more evident than in London; and somehow appear as though he is not a fully registered member of the established political class, some argue that the London mayor has just handed the Conservative strategist Lynton Crosby the ideal weapon for blunting the Ukip threat. Some also point to his earlier statements on same-sex marriage, or even Islam after the 7/7 bombings (“Islam is the problem”), as other things that might not have gone unnoticed in Ukip land.

But what do Ukip voters think of Johnson? There is no doubt that lots of them like him. When YouGov explored his image in March, it found Ukip voters were only second to the Conservatives in terms of the number who saw Johnson in a positive light – as someone who is charismatic, sticks to what he believes in, is honest, strong and in touch with ordinary people.

The same picture emerged in a poll by Lord Ashcroft last year, which suggested that when it came to healing divisions with Ukip, Johnson might have an immediate advantage over David Cameron: only 35% of Ukip voters saw the London mayor as arrogant compared with 59% for Cameron; only 20% saw Johnson as out of touch compared with 66% for Cameron; some 54% thought he understood Britain’s problems compared with 33% for Cameron; and a staggering 80% thought the mayor was a “people person” compared with 25% for Cameron. Overall, almost two-thirds of Ukip voters agreed Johnson was “different from most politicians, and in a good way”.

This is testament to Johnson’s unique qualities as a politician. He is the old Bullingdon comrade and close friend of Cameron, the man who most Ukip voters utterly disdain and see as representing everything that is wrong with modern-day Conservatism. He has family wealth and elite connections. He has never really worked outside of Fleet Street and Westminster, which senior Ukippers often attack. He remains largely in favour of Britain’s EU membership. He backed an amnesty for illegal migrants. He broadly supports high-speed rail. He has spoken positively about the possibility of further EU enlargement to include Turkey, home to some 75 million Muslims. And yet, majorities of Ukip voters say they like him. That a man who represents so much of what Ukip is against is still liked by its voters should worry Farage.

But is simply liking a politician enough to trigger a change of loyalty? That the answer may be “no” is revealed in a poll by Survation. It found that around 70% of Ukip voters thought Johnson was “likeable”. But at the same time, more than 60% of Labour and Liberal Democrat voters thought the same way. Johnson may have the potential to emerge as an effective and affable catch-all populist but when you boil it down, will he be able to prise away large numbers of Ukip voters? I see little in the way of convincing evidence.

While YouGov found that installing Johnson as leader of the Conservative party would improve its electability, only around one in five Ukip voters said this would make them more likely to vote Conservative (see graph). Even with a Johnson-led party, almost 80% of Ukip voters said they would still vote for a party outside the big three (presumably Ukip).

Graphic: YouGov

Other polls paint a similar picture – more than half of Ukip voters said having Johnson stand as their local MP would make no difference to their likelihood of supporting the Tories, while only one in three said they would be more likely to vote Conservative if Johnson was its leader.

Johnson is liked among many Ukip voters and could have a significant impact among natural Conservatives who have been pushed into the arms of Farage by Cameron, especially if he is given a free role to campaign in some key marginals. But most of Ukip’s voters seem beyond his reach, so the Conservatives will need more than Johnson to silence the rumbling revolt on the right.