The UK is marking one year since the first coronavirus lockdown was announced.
With the lockdown have come tough restrictions on socialising, closures of schools, pubs and shops with many rules currently still in place.
A minute’s silence will be held at midday as part of a day of reflection.
A year on, Mr Johnson has praised the “great spirit” shown since that moment and he offered his condolences to those who have been bereaved during the pandemic.
People are also being encouraged to stand on their doorsteps at 20:00 GMT with phones, candles and torches to signify a “beacon of remembrance”.
It is being organised by end-of-life charity Marie Curie.
The prime minister, who himself spent time in hospital seriously with with Covid, said the last year had taken a “huge toll on us all” and said the anniversary was an opportunity to reflect on the year – “one of the most difficult in our country’s history”.
On the day the first nationwide lockdown, it was announced that 340 people had died with the virus. That figure was later adjusted upwards when the way that figure is measured was changed during the summer.
Although it wasn’t a requirement in the early stages of the lockdown, the wearing of masks and face shield has become commonplace in the year that has followed.
From the start, ministers said they were putting their faith in the measures slowing down the impact of the virus while scientists in the UK and around the world found a way to combat what had become both a threat to health and to the population’s freedom to enjoy life.
That came with the development of several vaccines – and the UK has already seen 28 million people receive a first dose of either the Pfizer or Oxford-AstraZeneca vaccines.
Over the months, scientists, politicians and the public have assessed several key figures that are updated each day showing the number of new cases, the numbers in hospital, how many are being treated in ventilation beds, and how many have died within 28 days of a positive Covid test.
In recent weeks all of those measures are down – as a result of the lockdown and the effects of the vaccine rollout – but on Monday Mr Johnson warned that the effects of a third wave of coronavirus will “wash up on our shores” from Europe and said the country should be under “no illusion” the country will feel the effect of growing cases on the continent.
To mark the anniversary, London’s skyline will turn yellow with landmarks including the London Eye, Trafalgar Square and Wembley Stadium lighting up at nightfall.
Other notable buildings that will be illuminated include Cardiff Castle and Belfast City Hall, while churches and cathedrals will toll bells, light thousands of candles and offer prayers.
Wales First Minister Mark Drakeford will take part on a televised commemorative event, which will be broadcast on BBC One Wales and S4C at 17:15 GMT.
More than 250 organisations are supporting the day of reflection, including 82 leaders from religious groups and cross-party politicians, care organisations, charities, businesses, emergency services, public sector bodies and community groups.
Health leaders have paid tribute to their colleagues and the public for their support during the crisis.
Dame Donna Kinnair, general secretary of the Royal College of Nursing, said: “After a year of sacrifices and gestures, great and small, we are taking our turn to thank the public. In a time of loss and fear, they helped us to keep digging deeper.
“We will take a day to remember and reflect – as much about the future we want as the year we’ve had.”
Dr Susan Hopkins, Public Health England strategic response director for Covid-19, said the virus had “left no one untouched” and thanked public health workers “who have worked long and difficult hours to help keep the country safe”.