I am not a grass, however for those who are, the following info was taken from
https://www.taxevasionhotline.co.uk/
HM Revenue & Customs Tax Evasion Hotline
HMRC is committed to targeting tax evasion. We know some people don't pay their fair share of tax, which is unfair for the rest of us. Now you can help us do something about it.
The Tax Evasion hotline deals with income tax, corporation tax, capital gains tax, inheritance tax, VAT and National Insurance.
The Hotline can take your call on
0800 788 887 (Lines are open Monday to Friday 8am to 8pm, Saturday and Sunday 8am to 4pm), or you can submit a report here.
No information - however trivial it may seem -is too small. It could be the key to stopping fraudulent or criminal activity.
Time for someone to start sweating perhaps!