In the Ready Mixed Concrete case Judge McKenna said:-
"An obligation to do work subject to the other party's control is a necessary....condition of a contract of service"
Therefore in a contractual arrangement where the client does not have control over the worker, the contract will be outside IR35.
Control is about What, Where, When and How according to HMRC at ESM0519 and is also defined by Judge Mckenna in the Ready Mixed Concrete case as:-
"Control includes the power of deciding the thing to be done, the way in which it shall be done, the means to be employed in doing it, the time when, and the place where, it shall be done. All these aspects of control must be considered in deciding whether the right exists in a sufficient degree to make one party the master and the other his servant. The right need not be unrestricted."
What - If a worker can be told what to do in a succession of requests then there is control?
If however the worker is taken on as a specialist to do a specific type of task, and does that task only, then there may not be control over what the workers does as such.
Where - If a worker can be told where to do the work then that is an indicator a control, but where the nature of the work dictates where the work should be done HMRC suggest at ESM0522 that it is not a factor used to determine if there is control or not.
An example would be a contractor working on a banking system, for security reasons it would not be practical to do that work at home.
When - HMRC consider this a pointer towards having control over an employee but also recommend caution when doing so at ESM524 .
In the same way as where, if the premises is only open office hours then a contract can only be done during office hours.
This is not control it is the practical application of a contract.
How - HMRC define the How as the ability of the engage to determine the manner in which the worker completes the work.
But they also define in ESM0526 the fact that where this control over "how" the work is completed as a mild pointer to self employment.
The case law in regard to control still focuses on the fact that for there to be control then there must be sufficient control whereby one person is in the position of being a servant to a master, without this degree of control there can be no contract of service , ( employment ).
Both Castle Construction (Chesterfield) Ltd v Revenue & Customs [2008] and Mark Andrew Lewis (t/a MAL Scaffolding v Revenue & Customs [2006] are useful cases on control.
In the Castle case Special Commissioner Howard Nowlan decided that:-
91. On the perhaps more critical question of whether the Appellant, or indeed the principal contractors, told the bricklayers how to lay bricks, it was never suggested that they did.
Since many of the workers were, I understand, highly skilled and experienced, I imagine that they needed no control in this regard and would most certainly not have welcomed it.
Rather as Special Commissioner Mr. Williams concluded in MAL Scaffolding v. HMRC SPC 527 in 2006, the bricklayers were probably as fiercely independent as the scaffolders were in the MAL Scaffolding case, and would have been reluctant to accept control from anyone as to how they actually did their job.
92. Beyond the fact therefore that the principal contractors ensured that the architect's plans were followed, and rather obviously that walls were not put in the wrong place or built in the wrong sequence, there seems to have been little relevant exercise of control that can have much influence on my decision.
It will be important for any Professional Contractor and Freelancer to make sure that if they are relying on the lack of control in their contractual clauses and their position as a specialist; their practical day to day working arrangements support their contention.
Wherever possible always keep documentation and evidence of where control is not exercised by your client.
For further clarity you may wish to have your understanding of the practical arrangements in place in relation to control confirmed by your client and your staffing company in a confirmation letter.