More than 110,000 Britons are to receive a letter on their doormat about a Covid-19 study

Members of the public are being encouraged to join the study if they receive a letter.

At present, researchers are regularly testing 28,000 people, but officials announced plans last week to expand the programme to include 400,000 across Britain.

As part of the expansion of the study, the ONS has written to more than 110,000 people across the UK asking them to take part in the Covid-19 Infection Survey.

The survey aims to act as a surveillance tool to look out for coronavirus hot spots, and may help in spotting any potential second wave.

The survey also provides data on the types of people who are more likely to be infected, and could be key in highlighting numbers who are infected but have no symptoms.

Participants from private households, with or without symptoms, provide regular nose and throat swabs on a regular basis. These are analysed to see whether they have contracted the virus.

Some people are also asked to provide a blood sample which looks for antibodies.

Professor Sir Ian Diamond, the UK’s National Statistician, said: “The coronavirus has affected all our lives.

“We’re gradually returning to something more like normal life, but if that’s to continue we need to be even more vigilant for further outbreaks.

“One of the most important surveys we’ve ever run at the Office for National Statistics will help do that.

“You can be tested once a week for the first month and up to once a month after that.

“We’ll send a trained visitor to your home to make sure the test is done properly and safely. Then they’ll take away the samples for analysis and we’ll pass on the results to your doctor.”