HMRC

There are reports of fraudsters 'cloning' HMRC phone number in arrest warrant scam. The number appears to be a genuine HMRC call but is actually a scam to persuade people to transfer cash.
You can read about it here news.sky.com/story/fraudsters-cloning-hmrc-phone-number-in-arrest-warrant-scam-11542656

Having said that, I did once receive a phone call at 8.30 am in the morning from someone saying they were from HMRC advising that I needed to pay back a (to me) very large sum of income tax. I immediately dismissed it as a scam, and rang my accountants to check. They used a hotline to HMRC and came back to me to say the call had come from HMRC and they would dispute the amount with them. Turned out to be my accountants error, and I did have to pay back a lot of money, but I was appalled that HMRC think it is acceptable to ring at that time of day and demand money! Wish I could have left them on hold of an hour and a half!

There are a few earlier threads about this.
Type HMRC scam into the search box - top right of the page.