Households with a landline number have been told to be wary of calls from scammers posing as HMRC, following increased reports of phone scams.
The tax authority received more than 60,000 reports of phone scams in the six months to January 2019 - an increase of 360% on the previous six months.
According to Ofcom, nearly 26 million homes in the UK have a landline, which could put them at risk of being targeted by scammers, especially if their number is listed in the telephone directory.
HMRC says it will only ever call taxpayers to ask for a payment on a debt they are already aware of.
Mel Stride, Financial Secretary to the Treasury, said:
"We have taken major steps to crackdown on text and email phishing scams leaving fraudsters no choice but to try and con taxpayers over the phone.
"If you receive a suspicious call to your landline from someone purporting to be from HMRC which threatens legal action, to put you in jail, or payment using vouchers, hang up and report it to HMRC who can work to take them off the network."
The Revenue urges people to report suspicious phone calls to phishing@hmrc.gsi.gov.uk or call Action Fraud on 0300 123 2040.