“Subject to” is one of those bits of technical language that can easily cause misunderstandings. It comes up frequently in legislation and often leads to mistakes.
A rule that is described as subject to something else, is subordinate to that thing. So, if Rule A is subject to Rule B, Rule A is subordinate to Rule B.
In other words, it will take effect, only so far as Rule B does not apply.
This is much easier to see in practice. For example, s98A(1) Employment Rights Act 1996 reads:
98A(1) An employee who is dismissed shall be regarded for the purposes of this Part as unfairly dismissed if—-
(a) one of the procedures set out in Part 1 of Schedule 2 to the Employment Act 2002 (dismissal and disciplinary procedures) applies in relation to the dismissal,
(b) the procedure has not been completed, and
(c) the non-completion of the procedure is wholly or mainly attributable to failure by the employer to comply with its requirements.
What this means is that, if one of the statutory dismissal procedures should have been followed, but wasn’t completed and it is the employer’s fault, the employee has been automatically unfairly dismissed.
s98A(2) goes on:
s98A(2) Subject to subsection (1), failure by an employer to follow a procedure in relation to the dismissal of an employee shall not be regarded for the purposes of section 98(4)(a) as by itself making the employer’s action unreasonable if he shows that he would have decided to dismiss the employee if he had followed the procedure.
This creates a statutory defence. If an employer followed an unfair procedure, but can show that he would have dismissed anyway, the employee has not been unfairly dismissed.
However, subjection (2), is subject to subsection (1). So it cannot override the rule about automatic unfair dismissal.
So, there is a statutory defence if an employer runs an unfair procedure, but dismissal would have occurred anyway – unless there is a breach of that statutory dismissal procedure.