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Boris Johnson has pledged to halt hikes on "sin taxes," which include levies on tobacco, alcohol and sugar.

The frontrunner in the race to become prime minister committed to review the effectiveness of such taxes and to ask whether they unfairly hit those on low incomes.

The Tory MP also vowed not to introduce new ones until the review has been completed, as he hailed Brexit as an opportunity to examine tax policy.

Mr Johnson's campaign cited taxes on products high in salt, fat and sugar as examples, as the commitments were revealed on Wednesday.

His team did not immediately say whether the review would also include cigarettes and alcohol taxation.

Mr Johnson said: "The recent proposal for a tax on milkshakes seems to me to clobber those who can least afford it.

"If we want people to lose weight and live healthier lifestyles, we should encourage people to walk, cycle and generally do more exercise.

"Rather than just taxing people more, we should look at how effective the so-called 'sin taxes' really are, and if they actually change behaviour.

"Once we leave the EU on October 31, we will have a historic opportunity to change the way politics is done in this country.

"A good way to start would be basing tax policy on clear evidence."

England's chief medical officer has been considering taxing all unhealthy foods to tackle childhood obesity by discouraging parents from buying them.

Professor Dame Sally Davies said she wishes to incentivise healthy food sales, potentially subsidising them by charging more on unhealthy products.

A report by Dame Sally is due in September and was commissioned by a key ally of Mr Johnson's, Health Secretary Matt Hancock.

The sugar tax on soft drinks was introduced in April last year, and has been celebrated by experts including the Royal College of Paediatrics and Child Health.

Chief executive of Action on Smoking and Health Deborah Arnott said any move away from current tobacco taxing would be a "grave error".

"Smoking kills more than 100,000 people in Britain each year. And the evidence from other countries is clear, when taxes stop going up, smoking rates are likely to stop going down," she said.

"Making tobacco less affordable via taxation is considered to be the most effective means of discouraging young people from starting to smoke and helping adult smokers to quit.

"That's why this Government and its predecessors have implemented an escalator for tobacco taxes which increases prices above inflation at every Budget.

"To move away from that policy now would be a grave error."

Cancer Research UK chief executive Michelle Mitchell stressed the significance of the taxes and praised their success in lowering smoking rates and removing sugar from diets.

"Taxes on less healthy products do have a positive effect," she said.

"They have been highly effective in bringing down smoking rates to record lows, including within deprived communities, and the Treasury's own analysis showed the tax on sugary drinks took 90 million kg of sugar out of the nation's diet on day one.

"Physical activity is one way to lose weight but the Government also has a big role to play if we are to significantly reduce obesity levels."

The Obesity Health Alliance's Caroline Cerny said voluntary programmes for the food industry to cut sugar "have not had the same success" as the tax.

"The levy is supported by the public and welcomed by a wide range of health experts and is vitally needed as part of a package of measures to help create a healthier environment for everyone," she said.

Additional reporting by PA