Exclusive clarification from the Technical Consultancy Team, NHS Business Services Authority (NHS Pensions)
The regulations state that “a Locum practitioner may apply to join this Section of the scheme by sending an application (Locum forms) to the Employing Authority.”
Members have 10 weeks to pension this work. If they do not submit the forms in time then this work cannot be pensioned. So in effect they do have a choice, if they choose not to pension the work they do at Practice A then they just have to let the practice manager know that they are not going to pension it so that the 14.3% is not included in the cash envelope.
If you're a GP locum employed by a company, such as a locum agency or your own limited company, your are not eligible to contribute money earned in this way into the NHS superannuation scheme since you are the employee of a private company.