The government is planning to trial a Covid passport scheme to allow the safe return of sports matches, conferences and night clubs in England.

Passes would show if a person had been vaccinated, had a recent negative test, or natural immunity.

Trial events in the coming months will also explore how ventilation and testing before and after could help audiences return.

The pilots, which will include the FA Cup final, will last until mid-May.

But some of the listed events will not be trialling vaccination certification.

Meanwhile, Downing Street has confirmed countries will be in a risk-based "traffic light" system when foreign holidays resume.

The pilots will include the FA Cup semi final and final in London's Wembley Stadium, the World Snooker Championship in Sheffield, a mass participation run at Hatfield House in Hertfordshire, and several events in Liverpool including an evening at a nightclub, a business conference and a cinema screening in the city.

The first pilot event will be a comedy night in Liverpool on 16 April where audience members will be tested for Covid before and after the show.

Prof Iain Buchan, of the University of Liverpool, will be helping to run testing for the Liverpool-based trials. He told BBC Breakfast that vaccination would not be a criteria for admission to these events.

He said taking part in the Liverpool pilots would involve "giving your consent to take part when you book a ticket; receiving text messages about hands, face, space, fresh air; minimising unnecessary contacts before the event; getting tested within 36 hours, ideally as close to the event as possible; ideally having a test earlier in the week".

Prof Buchan added: "Don't go on the day if you have any symptoms. All the events will be in very well ventilated places and the ventilation will be studied, and people will asked to minimise contacts and get another test five days after, for the purpose of research."

'Covid-status certification'

The NHS is said to be working on a system to allow people to demonstrate their status through an app or paper certificate.

The government said it was also working with clinical and ethical experts on exemptions for people for whom vaccination is not advised and repeat testing would be difficult.

No 10 said it did not want the scheme, which it is describing as "Covid-status certification", to be used on public transport or in essential shops.

Businesses in England which can reopen in the coming weeks, including pubs, restaurants and non-essential retail will not have to use the system for now.

However, sources say requiring a certificate to access hospitality further down the line - perhaps to reduce the need for social distancing - has not been ruled out.

Prime Minister Boris Johnson said: "We have made huge strides over the past few months with our vaccine programme and everyone in the country has made huge sacrifices to get us to this stage in our recovery from Covid-19.

"We are doing everything we can to enable the reopening of our country so people can return to the events, travel and other things they love as safely as possible."

Writing in the Sunday Telegraph, Cabinet Office Minister Michael Gove said certification for international travel will be an "inevitability", and it could also be a "valuable aid" in reopening parts of the domestic economy faster.

Mr Gove, who is leading the review into the use of Covid passports, said: "Unless the government takes a lead we risk others establishing the rules of the road. So where should the lines be drawn to help protect freedoms, respect privacy, promote equality and get us back to normality?"

Critics, including more than 40 Tory MPs and privacy campaigners, have suggested such a scheme could be "discriminatory and counterproductive".

Labour's Jeremy Corbyn and senior Tory Iain Duncan Smith are among a broad coalition of MPs who have pledged their opposition.

While the proposed plans cover England only, the government is discussing the scheme with Scotland, Wales and Northern Ireland.

Under the government's four-step plan to ease England's lockdown, legal limits on social contact could be lifted by 21 June, if strict conditions are met.

The government also outlined further details of its plans for a risk-based traffic-light system for international travel after the "stay in the UK" message comes to an end.

It said it will "help ensure the UK's vaccine progress isn't jeopardised and provide clear guidance for travellers".

International leisure travel will not be allowed until 17 May at the earliest.

After this point, travellers from countries in the green category will not have to isolate, although pre-departure and post-arrival tests will still be needed.

For countries assigned red and amber, restrictions would remain as they are now, with arrivals required to enter quarantine or self-isolation.

Downing Street said it was too early to predict which countries will be on which list over the summer.

The list of countries included in each category will be drawn up closer to the time, and the government continues to advise people not to book summer holidays abroad.

It added that more detail on international travel will be provided on Monday, along with information about a review into social distancing.

The review is examining how and when distancing requirements and the working from home guidance could be lifted and whether Covid certification could facilitate changes to the rules.

On Saturday it was announced that more than five million people in the UK have now received a second dose of a Covid-19 vaccine. The latest figures show an additional 246,631 second doses, bringing the total to 5.2 million.

First doses have been given to 31.4 million people.

It comes as the UK begins to relax some coronavirus restrictions.

England has allowed gatherings outside of up to six people or as two households since Monday, while the reopening of outdoor hospitality and all shops is planned from 12 April.

Rules on visits to care homes in England will also be relaxed from 12 April to allow two regular visitors indoors, the government has announced.

Wales, Scotland, and Northern Ireland have also begun to allow outdoor socialising.

But Mr Johnson has warned people against mixing with other households indoors over the Easter weekend, even if they have been vaccinated.