Adults in England will now be able to get a Covid-19 vaccine without an appointment at hundreds of walk-in sites that have opened amid a resurgence of new cases, local media reported.

In the "grab a jab" campaign, those aged 18 and over can turn up at the National Health Service (NHS) drop-in sites, including football stadiums, theatres, supermarket car parks and shopping centres, Xinhua news agency quoted a report published in the Guardian newspaper on Saturday.

The vaccine hubs are open to people having their first dose but can also provide second jabs for the over-40s who had their first at least eight weeks ago, or at least 12 weeks ago for the under-40s, according to the report.

More than 43.8 million people in Britain have been given the first jab of the coronavirus vaccine while more than 32 million people have been fully vaccinated with a second dose, according to the latest official figures.

Prime Minister Boris Johnson has announced a four-week delay to the final step of England's roadmap out of COVID-19 restrictions until July 19, amid a surge in cases of the Delta variant.

Britain reported 35,204 new cases of the Delta variant in the past week, a 46 per cent increase, Public Health England (PHE) said.

It added that the Delta variant now comprises 95 per cent of all sequenced cases.

Recent data published by the PHE showed the AstraZeneca vaccine is 92 percent effective against hospitalisation from the Delta variant after two doses, and the Pfizer vaccine is 96 per cent effective.