Timing the switch against a running assignment
Leaving an umbrella part way through an assignment is a contractual question before it is a tax one. The agency has to agree to contract with a company rather than pay you through a provider on its preferred supplier list, the end client has to accept a personal service company, and the umbrella employment has to end on notice. Get the order wrong and there is a week with nothing payable in the chain. On whether the move is worth making, see when umbrella to limited makes sense.