Emma Walmsley has laid out plans to overhaul GSK into a leaner business with “more edge” that fast-tracks the development of blockbuster drugs and prioritises growth in the US, in her first set of interim results as chief executive.

As part of a new £1bn cost-cutting programme, the FTSE 100 firm will ditch 30 commercially unattractive drug development programmes and consider the sale of its rare diseases business.

It also plans to offload more than 130 drug brands, more than a fifth of its total, with sales of almost £500m. Drugs losing support include treatments for diabetes and rheumatoid arthritis.

Instead Ms Walmsley wants GSK to plough four fifths of its R&D cash into “priority” therapies with more profit potential in respiratory, HIV and its fledgling fields of oncology and immuno-inflammation.

“It’s about putting science very much at the core of our business and prioritising the strengthening of the pharma pipeline,” she said.

Investors welcomed the restructuring but were disappointed Ms Walmsley did not take the opportunity to upgrade financial guidance to 2020 despite the fresh round of cost-cutting, pushing GSK’s share price down 3pc in afternoon trading following the results announcement.

The firm also downgraded its earnings per share forecast for the full-year from 5-7% to 3-5%, reflecting the purchase last month of a $130m (£100m) US priority review voucher for a potential new HIV treatment.

The reiterated 2020 guidance, first given in 2015, is for sales growth of low-to-mid single digits and adjusted earnings of mid-to-high single digits on a constant currency basis.

Investment bank Goldman Sachs commented in a note: “The lack of upside to previous 2020 guidance is disappointing on the margin”.

GSK share price

Ms Walmsley, who took the helm from Sir Andrew Witty in April, said the company’s culture needed to change to improve financial performance: “We need to bring more edge, more of a performance focus, more accountability, more pace into our decision making and more cash consciousness.”

She also said she would make "the US number one” in her expansion plans, with GSK’s businesses in emerging markets to be reviewed.

The US emphasis was “nothing to do with Brexit”, Ms Walmsley said, but she stressed the UK’s £60bn drugs sector needed “at least two years” or “as long as possible” to prepare for the UK’s withdrawal from the EU.

She said investors could expect further changes in the “top 200” roles in the company after the recent major hires of Luke Miels from AstraZeneca to run the drugs business and former WalMart executive Karenann Terrell as chief digital and technology officer.

Axed | Clinical drug programmes GSK is ditching

She also reiterated she would not break up GSK – which has three divisions in pharmaceuticals, consumer healthcare and vaccines – despite calls to do so by star investor Neil Woodford, who dumped his £1bn stake in the company last month.

The streamlining of the drugs business, which accounts for more than half of GSK’s £27.9bn annual sales, comes after Ms Walmsley announced plans to cutback the firm’s consumer healthcare division last week, including selling century-old drinks brand Horlicks and cutting 320 jobs. These changes are part of the £1bn cost-cutting plan.

GSK’s half-year sales were up 15pc to £14.7bn, up from £12.8bn the previous year, in line with expectations, while net profits hit £1.3bn, slightly ahead of analyst forecasts.

The dividend was held at 80p for this year and next.