Flexible salary arrangements have HMRC approval to provide for statutory future benefits including pension, holiday pay, maternity pay, sick pay and others, all of which are paid subject to PAYE regulations.

Employees are not obliged by any law to draw the maximum possible salary. You can defer potential salary to build reserves for future pay and benefits. Umbrella companies cannot do this. The only UK tax requirement is that all payments to you from your work on assignment must be subject to PAYE.

IR35 requires contractors to be in a payroll with a contract of employment. In a payroll you are compliant with IR35/OPWR because there is no intermediary. Intermediaries Legislation is not applicable without an intermediary. The end client has no liability for unpaid payroll taxes because you are in a contractual payroll. This is the same for consultancy firms, umbrella companies and all other contractual employers.

CM is the employer paid by the client. The contractor is the employee paid by CM. There are regulations to control the margin when an employment agency is an intermediary. This does not apply when a consultancy firm is arranging an assignment for an employee. Highly skilled contractors can opt out of the agency regulations. Employee and employer are free to agree terms.