People should not “squander the gains” made against coronavirus in recent months, the head of NHS England has warned ahead of lockdown restrictions easing on Monday.
NHS England national medical director Prof Stephen Powis said “enormous progress” had been made, but it “does not mean job done”.
Outdoor gatherings in England are allowed from Monday.
Boris Johnson has said the roadmap for easing restrictions remains on track.
But writing in the Sunday Telegraph, Prof Powis warned that coronavirus could still “wreak more havoc and ill-health on a significant scale”. He cited concerns over variants.
While there are thousands of different versions, or variants, of Covid-19 circulating, those that are of particular concern were first detected in the UK, South Africa and Brazil.
Several European countries are already battling a third wave of coronavirus infections – the effects of which Mr Johnson said will “wash up on our shores”.
There also remain ongoing tensions over vaccine exports on the continent.
However, the prime minister has insisted that there is “absolutely nothing in the data” to discourage him from easing restrictions as planned on Monday.
Prof Powis said: “We’ve made enormous progress that we need to build on and not squander the gains we’ve made.”
He added: “We need to hold our nerve and drive for the line, so everyone can get back safely and soon to our normal lives.”
In England from Monday, the stay-at-home rule is ending and groups of up to six, or two households, will be allowed to meet outside – including in private gardens.
The next stage – due no earlier than 12 April – will allow non-essential retail, restaurants and pubs to reopen in England.
Meanwhile, NHS England is urging those aged between 50 and 69 to get their first coronavirus vaccine if they have not already.
Three quarters of 50-54-year-olds have received the vaccine – up from half in the last week.
NHS England said more than 25 million people have received their first dose of a vaccine, and 2.5 million have had their second dose.
Across the UK, more than 29 million people have received at least one dose of a coronavirus vaccine, and more than three million have had their second jab.
How are rules changing on 29 March in England?
People will be allowed to meet outside – including in private gardens – in groups of up to six, or as two households (with social distancing)
The stay-at-home rule is ending, although the government is urging people to stay local as much as possible; holidays away from home are still not allowed
Outdoor sport facilities will reopen, including golf courses, tennis and basketball courts, and outdoor swimming areas
Formally organised outdoor sports can restart
Weddings can take place, attended by up to six people
Wales became the first UK nation on Saturday to lift travel restrictions within its borders, allowing unlimited travel within the country.
Scotland’s stay-at-home rules become “stay local” on Good Friday and Northern Ireland’s stay-at-home message is to be relaxed on 12 April.