Boris Johnson is the early favourite among grassroots Tories to succeed David Cameron as leader, according to a poll conducted by Conservativehome.

The poll of 1,419 Conservative activists showed 32% back Johnson, eight points ahead of his nearest rival, former leader William Hague (24%), with education secretary Michael Gove on 19% and David Davis, who lost out to Cameron in 2005, on 10%.

The findings make dismal reading for George Osborne, who languishes in eighth place on 2%, following a difficult few months that began with his unpopular March budget and persists under grim economic data.

The poll was published four days after the London mayor showed his cheerleading qualities by whipping up a mass crowd in Hyde Park who had come to see the last leg of the Olympic torch relay, prompting the raucous chanting of his first name.

It coincides with a separate report by the Independent revealing a slump in Tory party membership, with latest estimates putting the numbers at between 130,000 and 170,000, compared with almost 300,000 shortly after Cameron succeeded Michael Howard as leader.

The poll of party activists showed Cameron was still the first choice to lead them into the next general election, though fewer than half backed him (49%). Johnson was second (18%), followed by Hague (12%) and Davis (10%), with Osborne trailing again.

Though Johnson is rumoured to lack widespread support among the parliamentary party as a potential successor to Cameron, his supporters point to his re-election as London mayor in May in a set of local elections which otherwise made grim reading for the Tories.

The mayor, as the chairman of Transport for London, is responsible for ensuring that disruption to commuters is kept to a minimum during the Olympics – reports from the Games's first Monday suggested this had begun promisingly.

Tim Montgomerie, editor of Conservative Home, said of Johnson's popularity: "He is a Eurosceptic who doesn't just love his country but loves its people too, whatever their politics, colour, religion or sexuality. David Cameron is comfortable with modern Britain too, but, to adapt one of Mr Johnson's own expressions, Boris zoinks off the Geiger counter of positivity. He hugs the nation and smothers it with rhetorical kisses."

The poll also showed pessimism among Tory members about the next election, with more than half (53%) predicting Labour will be back in office in 2015, compared with 47% who backed their own party.

Members see a Labour-Liberal Democrat coalition as the most likely outcome (22%), with 20% expecting an overall Labour or Conservative majority and 19% predicting a minority Tory government. Eleven percent predicted a minority Labour government and 8% a second Con-LibDem coalition.

Just 1% of Tory members wanted the coalition with the Liberal Democrats to continue beyond the next election – 20% want the relationship to end soon as possible, ideally this year.

The most favoured course (41%) was for the coalition to end shortly before the election so the two parties can set out their own plans, while 19% wanted it to continue right up to the election.