When IR35 was introduced in 2000, it was the contractor’s responsibility determine their IR35 status. This was changed in 2017, when end hirers in the Public Sector became responsible for assessing a contractors IR35 status instead.
Before 2017, the responsibility for determining employment status rested with the contractor as a director, working through a PSC. All tax was therefore taken from the PSC directly and processed via their own PAYE account.
However, this was changed in April 2017, where Public Sector organisations were required to undertake the assessment of their contractors themselves. From April 2021 Private Sector end hirers are required to undertake IR35 assessments on their contractor’s behalf.