The use of Covid-19 vaccine passports and certificates has created an uproar in recent days as arguments for and against have been put to the government - and it's an issue being debated across the world.
The government is currently reviewing if Covid health certificates - where proof of a coronavirus vaccine, negative test or natural immunity will allow you to access a service - is feasible and ethical, with trials expected to be carried out this month.
The government has said a vaccine passport or certificate would not be required to access essential services such as health care or food shops.
The idea is being fiercely contested and Boris Johnson faces a substantial rebellion from his backbenches if he does press ahead with the measure.
It is expected some form of international vaccine passport system will be implemented in the coming months, but the issue of domestic versions is more complicated.
The prime minister previously acknowledged the “moral complexities” around bringing in a domestic vaccine passport scheme.
Similar arguments are playing out in countries across the world where proponents of vaccine passports say they will speed up the return to normality but opponents say they are potentially discriminatory and extend government intervention into daily life too far.
Vaccines minister Nadhim Zahawi explains how coronavirus certification trial will work:
While most nations are in trial phases, some have already begun implementing them.
Israel has been lauded for its successful vaccine rollout which is among the best in the world and the nation is quickly returning to normal.
In order to speed up the return to normal, the country has been using a 'green pass' system which allows people who have been fully vaccinated or recovered from Covid-19 to visit large gatherings like concerts.
It also allows vaccinated people to go on foreign holidays to select countries.
The pass can be either physical or displayed in a mobile phone app.
The tool has been used to encourage people to get vaccinated and so far more than 60% of the population have had their first jab.
Those who have not had both jabs do not have access to such benefits and vaccine rollout among Palestinians has been slow - intensifying arguments over inequality.
The passes are also unavailable to foreign nationals, completely curtailing Israel's tourism industry.
Denmark launched its 'coronapas' system to be used domestically over Easter, unlike Israel's, people who have been given a negative test can also get access to the pass.
The 'coronapas' is available via an app or in paper format to people who have either been fully vaccinated, have tested positive for Covid two to 12 weeks previously or negative over the previous 72 hours.
It aims to allow people to enter non-essential shops as well as hairdressers and driving schools.
The Scandinavian country hopes to use the system to speed up the opening of its economy over the next few months.
Businesses that allow citizens in without a pass face fines.
France, Germany, Spain
Like the UK, France, Germany and Spain are all currently trialling different internal Covid passport systems, but all have come under sustained domestic criticism for considering the move.
In France the government is understood to be trialling a health pass, similar to the UK's which would allow a person entry if they have had a vaccine or tested negative for the virus.
According to The Telegraph, Germany is considering a pass system for vaccinated people.
The German government has said it is planning to restore freedoms to people who have had both jabs and remove them from having to quarantine if they come into contact with the virus.
Jens Spahn, the country's health minister said the "current state of knowledge indicates that vaccinated persons probably no longer play a significant role in the epidemiology (i.e. transmission) of the disease".
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Spain is also understood to be trialling internal vaccine passports as well as ones for foreigners who wish to visit the country.
Spain is eager to allow tourists to visit and has said it will implement the system from May.
All three nations as well as Denmark are also signed up to the wider EU vaccine passport plan.
What is the EU planning?
The European Union is currently working on a plan to allow vaccinated people and those who have tested negative to cross borders between members states.
The large logistical challenge required in getting the system up and running has presented a problem for the bloc as many states wish to allow free travel again as soon as possible.
The bloc is hoping to rely on a QR code to allow quick access across borders, but would require everyone to have a smartphone, as well as the testing system to be similar across all the member states.
Over in America, the issue of vaccine passports has fallen to individual states to decide whether to implement them.
The governors of several states have moved to outlaw them completely, while others have stated their intent to use them.In New York, a government-sponsored vaccine passport called the Excelsior Pass is being introduced. The smartphone app will show whether someone has been vaccinated or recently tested negative for coronavirus.
Meanwhile, in Kansas the Democratic governor has said their state has no interest in implementing vaccine passports while the Republican leader of Florida issued an order last week banning businesses from requiring customers to show proof they have been vaccinated.
The Biden administration has said there will be no federally mandated vaccine passport but is thought to be trialling a set of standards that could be used in all states.
White House Press Secretary Jen Psaki said last Friday that any potential vaccine passports would be primarily directed by private businesses.