LONDON (REUTERS) - Prime Minister Boris Johnson urged Britons to be cautious as a stay-at-home order and some other lockdown measures are lifted in England, citing rising cases in other parts of Europe and the threat posed by new variants of the virus.

The government will also set up a new Office for Health Promotion to help tackle obesity, improve mental health and promote exercise. Mr Johnson himself said he was "too fat" when he became gravely ill with Covid-19 last year.

From Monday (March 29), up to six people, or two households, in England can meet outside while outdoor sporting facilities such as tennis and basketball courts can be used with social contact limits in place.

Britain's vaccination programme has been one of the most successful in the world but there are concerns over supplies, high infection rates in parts of Europe and the ongoing emergence of new coronavirus variants.

"We must remain cautious, with cases rising across Europe and new variants threatening our vaccine rollout," Mr Johnson said.

"Despite today's easements, everyone must continue to stick to the rules, remember hands, face, space, and come forward for a vaccine when called."

A new public information campaign showing how fresh air reduces the risk of transmission will run from Monday as part of efforts to remind people not to go indoors as they socialise.

The Office for Health Promotion aims at a joined-up approach between local, national authorities and the health service, according to the government, which said around 80 per cent of health outcomes were linked to factors like diet, smoking and exercise.

"Covid-19 has demonstrated the importance of physical health in our ability to tackle such illnesses, and we must continue to help people to lead healthy lives so that we can all better prevent and fight illnesses," said Mr Johnson.