If you have used a disguised remuneration scheme and had loans outstanding on 5 April 2019, then income tax and National Insurance contributions will apply under the 2019 loan charge.
This treats any outstanding amounts of payments as taxable income for the tax year 2018/19, and imposes reporting and payment obligations on both employers and employees.
You must ensure that the loan charge is settled in accordance with the legal requirements, or face penalties. HMRC has published detailed reporting and payment guidance here. There is also a settlement opportunity and settlement guidance.If you have used an umbrella payroll scheme and paid broadly less than 20% tax on the sums received, then you are at high risk of crossing the line from tax avoidance into tax evasion.