The Chartered Trading Standards Institute (CTSI) said it had received reports of scammers targeting the elderly and vulnerable, saying they were health officials doing door-to-door testing.

Katherine Hart, CTSI joint lead officer for doorstep crime, said: “There are unfortunately people who are willing to take advantage of those who are most vulnerable even at this unprecedented time when we should all be pulling together.

“Those who have been advised to avoid social contact as part of the measures to help stop the spread of the virus are particularly at risk of being taken in by these cold callers.

“Our message is not to open the door to anyone you don’t know or anyone calling ‘out of the blue’. Stay safe by only speaking to people you know and trust.”

The alert comes as part of the CTSI’s ongoing advice to the public about scams and rogue practices relating to the spread of the disease.

Earlier this week, it warned that opportunistic businesses were trawling social media and offering to carry out emergency repair work at inflated prices.

It advised people to agree on the price for any work upfront, make sure the agreement is put in writing and to use a trusted trader, or one they’ve used before.