HM Revenue and Customs is to write letters to around 50 professional UK football clubs as part of efforts to ensure they pay the minimum wage to the armies of staff they rely on delivering their match day experiences and team analysis.

Tax officials have warned clubs that failure to pay staff – such as mascots, ball boy supervisors, physio interns and performance analysts – could result in fines worth £5,000 and even prosecution.

The clubs are to receive the warning letters directly from tax inspectors, who will also be conducting spot checks on earnings. It is understood that the letters have been prompted following allegations by mascots that they were not paid.

The UK's national minimum wage laws make it illegal not to pay people classed as workers.

In April this year, Reading FC made headlines after it advertised a year-long internship that paid no salary or expenses.