Rishi Sunak has been heckled during a visit to a beer festival where he was seeking to promote a shake-up of the alcohol duty regime that will increase tax on a range of drinks.

“Prime Minister, oh the irony that you’re raising alcohol duty on the day that you’re pulling a pint,” publican Rudi Keyser yelled, as Mr Sunak toured the Great British Beer Festival in west London’s Olympia on Tuesday.

Mr Sunak has insisted the reforms centre on “backing British pubs” and that businesses and consumers will benefit from the post-Brexit alcohol duty changes, despite the increases on wine, vodka and canned beer.

First set out by Mr Sunak when he was chancellor in 2021, the new system aims to encourage drinkers to cut back by taxing all alcohol based on its strength, rather than the previous categories of wine, beer, spirits, and ciders.

He described the overhaul as “the most radical simplification of alcohol duties for over 140 years”, enabled by Britain’s exit from the EU.

But whisky distillers describe the changes as a “hammer blow” and brewers warn of a tax hike on bottles and cans.

Mr Sunak was pouring a pint of Black Dub stout at the stall of the Wensleydale brewery from his North Yorkshire constituency when he was heckled by Mr Keyser, a 46-year-old who runs a chain pub in London’s Wimbledon.

Mr Keyser, a former brewer, told the PA news agency that Mr Sunak’s claim that drinkers and businesses will benefit is just “smoke and mirrors”.

“It’s robbing Peter to pay Paul,” he said, insisting that consumers will see an increase in prices as a result of the changes.

“And he has the audacity to come and pull a pint for PR,” Mr Keyser added.

Another man shouted at the pint-pulling teetotal premier, who is famously a fan of Coke: “Prime Minister, it’s not Coca-Cola.”

In March’s Budget, Chancellor Jeremy Hunt also announced that the freeze on alcohol duty would end on August 1 and increase by inflation, at 10.1%.

The increase will see duty rise by 44p on a bottle of wine, which, when combined with VAT, will mean consumers will pay an extra 53p, according to the Wine and Spirit Trade Association (WSTA).

The Chancellor is cutting the duty charged on draught pints across the UK by 11p in August, effectively freezing or cutting the duty on beer poured from tap in the nation’s 38,000 pubs and bars.

Mr Sunak hailed the tax relief for pubs, which he called “such a special part of our country’s fabric” as he chatted to stallholders at the festival featuring hundreds of different brews.

He told reporters at the event: “Now that we’ve left the EU, we can ensure that the tax we pay for beer on draft in pubs is lower – less than the tax we pay for beer in the supermarket.”

He defended the reforms when asked about alcohol duty rising by 10.1% in line with inflation, saying the simplification of the system, which means “the lower the alcohol in the drink, the less tax you pay”, follows a “common-sense principle”.

The Prime Minister later appeared to mistakenly refer to himself as the chancellor during an interview with GB News at the venue.

Asked by the channel to name his favourite pub, he said: “Well I’m a teetotal chancellor but we’re delivering and backing our great British pubs with our Brexit pubs guarantee.”

The British Beer and Pub Association (BBPA) said brewers will pay 10.1% more tax on bottles and cans of beer from Tuesday, meaning tax will make up around 30% of the cost of a 500ml bottle.

Despite the draught freeze, the BBPA said the tax increase on packaged beer will add an extra £225 million of costs per year across the industry.

Scotch Whisky Association director of strategy Graeme Littlejohn said: “The 10.1% duty increase is a hammer blow for distillers and consumers.

“At a time when inflation has only just started to creep downwards, this tax increase will continue to fuel inflation and make it more difficult for the Scotch whisky industry to invest in growth and job creation in Scotland and across the UK supply chain.

“Rather than choosing to back an industry which the UK Government promised to support through the tax system, the Government has chosen to impose the largest duty increase in almost half a century, increasing the cost of every bottle of Scotch whisky sold in the UK by almost a pound and taking the tax burden on the average priced bottle to 75%.

“In a further blow, distillers will now face a further competitive disadvantage in pubs, restaurants and bars by being unfairly excluded from tax breaks available to beer and cider.

“Pubs and other on-trade businesses are about far more than beer and cider.”