For the first time since he became mayor of London on May 2, Boris Johnson has overtaken Conservative leader David Cameron in “favourability”, according to an opinion tracker published on www.politicshome.com.

Johnson scored a rating of 3, up from -7 at the end of April, while Cameron got rated 1, up from -5.

The PHI5000 tracker is based on replies from a politically balanced group of 5000 voters across the UK, who answer a survey every day for the site, which was launched in April and is powered by opinion pollsters YouGov.

The panel are asked daily questions on a rotation system, covering their attitudes to the whole political landscape. As part of this, politicshome tracks a wide range of political personalities, including Cameron’s and Johnson’s favourability ratings.

Because of the consistency of the sample and questionnaire of the tracker, the site is able to track subtle changes in public opinion, it says.