Scientists and politicians appear to be split on whether people in the UK should be wearing face masks to help slow the spread of coronavirus.

– What is the UK advice on face masks?

It is currently not compulsory to wear a mask or face covering and the UK Government is still considering evidence from experts on the Scientific Advisory Group for Emergencies (Sage).

But Scotland’s First Minister Nicola Sturgeon said her devolved government was now recommending wearing face masks in public in “limited circumstances”, including in shops and on public transport.

The new guidance from the Scottish Government, which is not mandatory, suggests wearing face coverings for the mouth and nose made of cloth or fabric, such as a scarf, and not surgical or medical-grade masks.

Public Health England (PHE) recommends masks for NHS staff and social care workers but does not suggest other people wear them outside.

London Mayor Sadiq Khan is among those calling for a change in advice to add “another layer of protection” to members of the public against Covid-19.

He has previously said: “Wearing a non-medical facial covering makes it less likely you may inadvertently give somebody else Covid-19.”

– Will the advice change?

Downing Street said the Prime Minister wanted to maintain a UK-wide response to coronavirus as far as possible but there was no hint of whether the Government would adopt the same policy as Ms Sturgeon.

But there have been growing calls for a change in advice, with Dr Chaand Nagpaul, chairman of the British Medical Association (BMA) council, suggesting the public cover their mouths and noses when going outside for essential reasons.

Another top doctor said it would make sense to advise the public to wear coverings on a voluntary basis and expects the Government to alter its guidance.

The chairman of the Royal College of General Practitioners Professor Martin Marshall said: “If (people) are coughing and spluttering then it makes complete sense to wear masks in order to protect other people.”

He told the BBC’s Today programme: “I think the guidance that we’re expecting to hear is that the wearing of face masks is a voluntary activity not mandated and it certainly makes a lot of sense to focus limited resources that we have at the moment on those who have greatest need and that’s the health professionals.”

– Are they effective?

Experts have cast doubt on the strength of the evidence on the benefits of face masks.

Last week, chief scientific adviser Sir Patrick Vallance said the evidence on face masks “has always been quite variable, quite weak and difficult to know”.

According to European scientists, there is no evidence that non-medical standard face masks or other covers offer protection to wearers.

The European Centre for Disease Prevention and Control says that a non-medical mask has a filter efficiency of between two and 38%.

But the World Health Organisation recommends face mask use for people who are taking care of a person with Covid-19, or if they are coughing or sneezing themselves.

– Are there enough masks for key workers and the general public?

NHS bosses have urged the Government to make sure that there are enough masks for medical staff before making any compulsory orders for the public.

Chris Hopson, chief executive of NHS Providers, which represents hospitals and NHS trusts in England, asked ministers to “fully assess” the potential impact on healthcare supplies.

He said: “There needs to be clear evidence that wearing masks, along with other measures, will deliver significant enough benefits to take us out of lockdown to potentially jeopardise NHS mask supply.”

– Will I be given a mask if they are made compulsory?

The Government has said it “can’t promise” everybody will be given a mask for free if the public are forced to wear them.

Matt Hancock was asked the question by former Labour minister Hilary Benn in the House of Commons, and replied: “I can’t promise that we will give everybody free masks, I mean that would be an extraordinary undertaking, and we do have to make sure that we have supplies available especially for health and social care staff, where the scientific advice throughout has been that the wearing of masks is necessary in those circumstances and we’ve got to make sure the provision is there for them.”

– Can I make my own mask?

Masks can be made from cloth materials found at home, or items that can be wrapped around the face such as a scarf.

Trish Greenhalgh, professor of primary healthcare at the University of Oxford, told a Royal Society of Medicine web briefing: “How do you make your own mask? You take two pieces of cotton, or a piece of cotton folded over, and you take a pantyliner or something like that [with] waterproof backing, you stick it between those.

“And then you hook it around the back of your ears.”

– What types of mask exist?

The main types of mask can be divided into three types – homemade cloth masks, surgical masks and N95 or FFP3 respirators used by healthcare professionals.

In the US, the Centres for Disease Control and Prevention (CDC) has recommended the use of cloth masks in environments where it may be hard to socially distance.

These can help prevent spreading the virus by coughing, sneezing or speaking.

Surgical masks do not create a seal on the face but are designed to prevent the spread of large droplets and protect medical staff from splashes.

N95 respirator masks can help prevent the spread of small particles, are tight-fitting to the face and can filter up to 95% of airborne particles, the CDC said.

While medical masks have clear evidence supporting their effectiveness, deputy chief medical officer Dr Jenny Harries urged the general public not to use them.

She said: “The number one thing is, we must leave our medical masks, if you like, for those people that need them at the front line, because there is clear evidence that that is beneficial.”