Britain is the only western nation other than the US where life expectancy has continued to fall following a flu outbreak in 2014-15.

Experts have compared the slump in life expectancy to post-Soviet Russia, and warned that sustained falls in life expectancy should be regarded as a 'major warning sign'.

Flu can be held responsible for just a third of the three-month drop since 2014, and scientists have urged for ministers to investigate the trend properly.

Experts have compared the slump in life expectancy to post-Soviet Russia, and warned that sustained falls in life expectancy should be regarded as a 'major warning sign'

Research carried out at the University of Southern California compared life expectancy in 18 western nations, which found 12 showed a fall in life expectancy during the bad flu season.

However only the UK and US failed to rebound, according to data published in the British Medical Journal.

It comes after The Times revealed life expectancy in some parts of Britain had plummeted by a year since 2011. Official figures revealed 10,000 more people died in the first two months of this year that expected - the largest jump since World War Two.

Jessica Ho, the leader author on the study, said: 'Life expectancy is a core indicator of conditions of health and wellbeing in a country.

'When progress in life expectancy stagnates or even reverses, it tends to be an important warning signal about conditions within a country. It's extremely important to understand why life expectancy has declined, particularly when the declines are sustained over multiple years, as is the case for both the UK and the US.'

However only the UK and US failed to rebound from 2014-15 slump, according to data published in the British Medical Journal

She added: 'This is the sort of thing that happens during epidemics, like the global HIV/AIDS epidemic, or in countries undergoing dramatic social and economic change, like Russia during the post-Soviet transition.'

The cause of the fall is disputed, with some citing loneliness, overstretched hospitals and a struggling healthcare system for older people.

Danny Dorling, of the University of Oxford, said: 'The decline in health outcomes that has become very clear after 2014 has not occurred before in the UK since at least during the Second World War.'

He added: 'My suspicion is that the UK cutting public spending far more than other states is one of the key reasons why the UK stands out like a sore thumb.'