How long does use of a substitute provide some IR35 protection for?

[dingdong]

I've used both a subsitute and a subcontractor this year whilst performing my current engagement.

If I now move onto a new statement of work for an additional project for the same client would that use of a substitution be considered part of the same engagement.... or are you effectively back to square zero on meeting the working practice tests anytime you have a newly signed contractual document?

The CEST tool previously mentioned engagement rather than contract hence my query.

[jamesbrown]

It applies to the hypothetical contract that seeks to describe the reality of your working practices (WPs). In other words, if you sign a new contract and the WPs don't change, then the earlier substitution would be supportive of your current WPs being outside. Of course, WPs can change, especially on long engagements, so the weight of this earlier evidence will inevitably diminish over time and you should keep up-to-date evidence in support of your current WPs.