Wearing a face mask has become about making a political statement rather than public health, a government scientist has said.

Prof Clifford Stott, of Keele University, told LBC: "We know that wearing masks, particularly in crowded, poorly ventilated environments, has a big impact on the levels of transmission that can take place.

"But also I think, particularly now, wearing a mask is also communicating to others about a sense of responsibility – and I think that’s a key issue in mask-wearing now, unfortunately."

Prof Stott, a member of the Scientific Pandemic Insights Group on Behaviours (SPI-B), added: "I think, unfortunately, it’s become almost a little bit politicised whether one wears one or not, which is I think a shame."

He said transport networks mandating the wearing of masks assisted him in "not feeling awkward wearing one".

Boris Johnson has said people should still wear a mask when in crowded areas, despite the laws on coverings being scrapped last month.

According to the Office for National Statistics (ONS), 92 per cent of people said they wore a mask in the last week.

Less than a third of those – 31 per cent – said they wore one on public transport, compared to 92 per cent of people who did so while shopping. Half of 16 to 29-year-olds said they wore a face mask on buses and trains, while only 22 per cent of the over-70s did so.

Prof Stott added: "I think the data that we do have show that the majority of the public do want to retain some legal infrastructure around there – so I think the latest data was around about 67 per cent of the population.

"I think this is a broader issue about how the Government is communicating that transmission no longer matters. I think the argument that we should be having here is that it’s about the way that the broader relaxation of the Government’s position over the virus is effectively communicating to people that transmission is no longer that important.

"Yet at the same time, of course, we’re seeing this rise and very heavy spread of the delta variant."

It came as Sadiq Khan, the Mayor of London, said failure to wear a face covering on the Tube should become a criminal offence.

Mr Khan called on the Government to allow a bylaw to be introduced by Transport for London (TfL) which would require masks to be worn on the capital’s public transport system.

Since the easing of restrictions last month, the requirement for a mask on London’s Tube lines has been a "condition of carriage" rather than a legal requirement. A bylaw would see TfL officers able to impose fines, in addition to current powers to prevent passengers from boarding.

Research by YouGov this week found that 79 per cent of English people want to bring back mandatory face coverings for public transport.

Despite restrictions being eased in Wales on Saturday, Mark Drakeford, the country’s First Minister, said masks would still be required on public transport and in shops.

Mr Drakeford told BBC Radio Wales: "In other parts of the world where mask-wearing was lifted, it’s having to be reintroduced again, as it was last week in the United States of America."