It is important to note that IR35 itself has not changed. HMRC has introduced new rules about the party who should determine the IR35 status. Currently, it is up to contractors in the private sector to establish whether or not their contract work is subject to IR35. From April 2020 onwards, this obligation will fall to the end-client rather than the contractor. The only exception to this will be ‘small companies’ as defined by the Companies Act 2006
Being outside IR35, you are a self-employed worker and no employment taxes are deducted at source. If you are deemed inside IR35, the relationship between you and your client is one of employment and employment taxes are due. The end-client will deduct income tax and employee National Insurance Contributions (NIC) from your gross payment. The end-client will pay the employer NIC.
HMRC has said it will not investigate IR35 applications retrospectively (looking back on past cases) unless there is evidence of fraud or criminal behaviour. HMRC will not carry out targeted campaigns into previous years when individuals start paying employment taxes under IR35 for the first time.