From a very brief google:
https://www.gov.uk/report-an-unregistered-trader-or-business
Seems like the government stance is suspicion is sufficient.
https://www.gov.uk/report-an-unregistered-trader-or-business
Report someone to HM Revenue and Customs (HMRC) if you think they’re evading tax.
Don’t try to find out more about the tax evasion or let anyone know you’re making a report.
Seems like the government stance is suspicion is sufficient.