now saying that IR35 is only determined by who pays a sub if one is provided.
It's a subtle difference but a very important one. You can replace an employee very easily, and you can offset some of their work to another worker equally easily. Neither is a substitution in employment law, which says, put simply, the substitute is a one-for-one replacement for the engaged worker under the same contract and Ts&Cs as the original worker and paid out of the original worker's income.
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