134(1)
A fixed term standard contract may not be varied except—
(a) by agreement between the landlord and the contract-holder, or
(b) by or as a result of an enactment.
134(2)
A variation of a fixed term standard contract (other than by or as a result of an enactment) must be in accordance with section 135.
134(3)
This section is a fundamental provision which is incorporated as a term of all fixed term standard contracts; section 20 provides that subsections (1)(b) and (2) of this section—
(a) must be incorporated, and
(b) must not be incorporated with modifications.