A fundamental term of a fixed term standard contract which incorporates any of the fundamental provisions to which subsection (2) applies may not be varied (other than by or as a result of an enactment).
This subsection applies to the following fundamental provisions—
A variation of any other fundamental term (other than by or as a result of an enactment) is of no effect—
A variation of a term of a fixed term standard contract is of no effect if it would render a term of the contract incompatible with a fundamental term (unless that fundamental term is also varied in accordance with this section in a way that would avoid the incompatibility).
Subsection (4) does not apply to a variation made by or as a result of an enactment.
This section is a fundamental provision which is incorporated as a term of all fixed term standard contracts...; section 20 provides that this section—