HMRC claim that compliance checks are normally triggered when there appears to be an error on your tax return. It could be that if you are a company, there is a large VAT claim. If only a small amount of tax is declared by a business with a very high turnover then this could also trigger a tax investigation. There are other things that could also lead to an HMRC Investigation. These include a tip-off to HMRC by an ex-business partner, friend or neighbour, your business receives a large amount of cash as payment, or you experience a large drop in income or a dramatic increase in costs.