The boss of Britain’s largest drugmaker has said the US is its “biggest priority” amid pressure from Donald Trump to slash prices for US citizens.

Dame Emma Walmsley, who will step down from GSK at the end of the year, praised the US and said the group is working with the Trump administration after it launched a campaign to address high drug prices.

Shares in pharmaceutical companies surged on Tuesday after rival pharma group Pfizer struck a deal with the White House to lower prices for some of its medicines. Mr Trump has also demanded greater investment in the US from drug companies after introducing a 100pc tariff on branded drugs made abroad.

The Pfizer agreement, which averts tariffs for three years, triggered a relief rally that sent shares in AstraZeneca up 11.2pc, as it reclaimed its place as Britain’s most valuable company. GSK shares jumped by 6.2pc.

Dame Emma admitted GSK was “betting big on the US” after she pledged during Mr Trump’s UK state visit last month to invest $30bn (£22bn) in America over the next five years.

She said: “Absolutely GSK is engaging constructively. The markets also view it this way, as it’s about constructive dialogue between the industry and the Government.

“The US is by far the biggest priority market for our industry because the US is the best country in the world to discover and develop innovation.”

As the country’s largest drugmaker, GSK has become a national champion for the UK pharmaceutical sector, despite generating only a small proportion of its revenues in the UK.

Britain represents just 2pc of the £65bn drugmaker sales, compared to 52pc in the US.

Despite this, Dame Emma said the group would not ditch its listing on the London stock market for New York. GSK’s shares have fallen overall in the eight years since she took over in 2017.

“I’m not getting distracted by the listing questions that everyone keeps asking about,” Dame Emma told Bloomberg’s Women, Money & Power conference.

“Our listing location doesn’t distract from where we allocate our capital in terms of investments. There are no plans for that.”

She also said there had been “zero engagement” on a potential merger with any other UK pharmaceutical company.

Her comments come days after AstraZeneca stoked fears that Britain’s biggest drugmaker could quit London after it announced plans to list shares on the New York Stock Exchange.

In a shake-up announced on Monday, the FTSE pharmaceuticals giant said it would upgrade its US listing to ensure it is equally as important in New York as it is on the London Stock Exchange.

Bosses said the move would make it easier for the company to raise money from US investors, describing it as “a global listing for global investors in a global company”.

Analysts at AJ Bell said the decision hinted “at the possibility of a more dramatic shift at some point in the future”.

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