Boris Johnson undermined one of his cabinet supporters last night by pledging to drop an obesity policy being championed by Matt Hancock, the health secretary.

In a sign of confusion at the heart of the campaign, the Tory leadership contender announced that he would order a review into the government’s sugar tax and veto proposals to extend it to milkshakes.

The former foreign secretary’s announcement came days after Mr Hancock circulated plans to the cabinet that suggested extending the tax to sugary milk products.

The proposal, signed off by Mr Hancock and seen by The Times, described the sugar tax as “hugely successful”. It is understood that Mr Hancock, who is backing Mr Johnson, was not made aware of the contender’s announcement in advance.

Boris Johnson undermined one of his cabinet supporters last night by pledging to drop an obesity policy being championed by Matt Hancock, the health secretary.

In a sign of confusion at the heart of the campaign, the Tory leadership contender announced that he would order a review into the government’s sugar tax and veto proposals to extend it to milkshakes.

The former foreign secretary’s announcement came days after Mr Hancock circulated plans to the cabinet that suggested extending the tax to sugary milk products.

The proposal, signed off by Mr Hancock and seen by The Times, described the sugar tax as “hugely successful”. It is understood that Mr Hancock, who is backing Mr Johnson, was not made aware of the contender’s announcement in advance.