It comes as officials announced plans for new real-world trials of the impact of weight-loss jabs on worklessness.

Researchers will examine the ‘real-world effectiveness’ of anti-obesity treatment Mounjaro, also known as tirzepatide, over a five-year period.

A study by Health Innovation Manchester and Lilly – the world’s largest pharmaceutical company – will examine the drug’s impact on weight loss, diabetes prevention, the prevention of obesity-related complications, and the impact on NHS use.

The research will also assess whether the drug will reduce worklessness and whether it has any impact on cutting sick days among employed people.

Experts said the results of the trial, which will take place in Greater Manchester, will ‘potentially inform the UK’s care-pathway approach to the treatment of obesity’.

Mounjaro, manufactured by Lilly, has been hailed as the ‘King Kong’ of weight-loss jabs after a previous study found people taking the drug, along with support to make changes to exercise and diet, lost an average of 21% of their bodyweight over a 36-week period.

NHS officials have suggested that the roll-out of the drug across England will need to be staggered due to anticipated high levels of demand.

Nearly a quarter-of-a-million people are expected to receive the Mounjaro jab over the next three years, officials have said.

NHS leaders have proposed that people who will get the ‘greatest clinical benefit’ should be first in line for the drug, which is to be offered with a ‘wraparound package’ including diet and exercise support.

The National Institute for Health and Care Excellence (Nice) will publish its final guidance on Mounjaro and obesity later this year.

Mounjaro, which is made by Eli Lilly, is a glucagon-like peptide-1 (GLP-1) agonist, a family of medications that help manage blood sugar and are used to treat type 2 diabetes and obesity.

Other GLP-1 agonists include semaglutide – sold under the brand names Wegovy, Ozempic and Rybelsus.

These medicines have seen a number of supply issues in recent months.

In his letter, the Health Secretary said: ‘The long-term benefits of these drugs could be monumental in our approach to tackling obesity.

‘For many people, these weight-loss jabs will be life-changing, help them get back to work, and ease the demands on our NHS.’

A recent report by the NHS Confederation and the Boston Consulting Group highlights how economic inactivity in the UK has risen by 900,000 since 2020, with 85% of this due to people who are long-term sick.

The authors said that two main age groups were driving the rise in long-term sickness coupled with economic inactivity – 18 to 24-year-olds and 50 to 64-year-olds, with the older group accounting for 55% of all inactive long-term sick people.

In both groups there had been a ‘rapid rise’ in people reporting multiple health conditions, the report found.

Musculoskeletal (MSK) and mental health issues account for around 50% of all conditions reported by people who are long-term sick and economically inactive.

Mr Streeting insisted individuals will need to remain responsible for taking ‘healthy living more seriously’, as the ‘NHS can’t be expected to always pick up the tab for unhealthy lifestyles’.