Alex Peebles, Public Law solicitor at Duncan Lewis, discusses the legal challenge he is leading on behalf of locum doctors and nurses caught up in the IR35 dispute. Alex explains that the Check Employment Status for Tax (CEST) online tool on the HMRC website, used by employers to determine the status of all individual workers based on particular factors, is flawed in that it does not take into account all factors. Significantly, CEST does not test for the mutuality of observation (MOO) which is designed to identify the existence of an employer relationship. MOO directly links to the application of IR35 to the individual’s case. In absence of this the results may be biased, meaning a worker can be recognised as within IR35 when they are not. Presenter Paul Lewis asks why locum or contracted workers should receive better tax than other employees within their sector. Alex responds by pointing out that when assessed some workers have been accepted by HMRC to have some engagements that have not been caught by IR35. Alex states: “It seems a little strange then that [locum and contracted workers] are now in a position because of a change – not in the underlying basis of IR35 – but in responsibility for making the assessment, that all of a sudden they find themselves in a much worse off tax position.”