[varispeed]

It's worth noting that length of the contract or number of clients is irrelevant from the IR35 point of view. It's a common myth.

As an employee you can just as well have many short employments and work for multiple employers.

[Lio]

From what I understand about IR35 it's also applied on a contract by contract basis.

So you could run one contract Inside IR35 at the same time as another is Outside IR35.

HMRC refuse to fully disclose exactly how they deem a contract to be Inside or Outside but I always go with how much control I get and if I'm billed solely on time or deliverables. Even then there's no certainty, you just have to submit the accounts and hope for the best.

[logisticpeach]

It's not so much that they refuse to disclose the methodology, it's that there is no methodology. The rules are (I suspect intentionally) vague and the degree to which any given factor (duration of contract, working practices etc.) applies, seems to vary from case to case.

This creates an environment of great uncertainty for freelancers, but also one where HMRC can never be sure themselves, if they're properly pursuing those accused of being in breach.

They seem to regularly lose many of these cases on appeal when a (presumably) fair minded judge is asked to look at the facts.