Re: Wait? I'm a contractior now?
My biggest issue with this particular ruling is the one of substitution.
In some cases, especially in the security field, it would be nigh on impossible to invoke a right of substitution for several reasons, and a client may want a particular contractor 'as a person' because of the specific knowledge they can provide which others (such as an alternate) would not.
I don't know why this is a particular focal point for IR35, because I can think of other roles and scenarios where someone is taken on for their specific skill-set and knowledge where it is clearly a business relationship, not one of employer/employee.
For example, if you hired a specific architect who specialised in a particular type of design, it would be impossible to for the architect to put someone else in his place unless they could satisfy the client that they had the same design specialisations as the original architect - in that scenario the client has the right of veto - but I doubt anyone would claim the architect was employed by the client.
This is why I hate IR35, it just isn't consistent enough across all cases to be predictable, and therefore manageable in terms of risk.