Nothing in this Part of this Act affects prejudicially the right to enforce any lessor’s or lessee’s covenants, agreements or conditions (including a valid option to purchase or right of pre-emption over the reversion), contained in any such instrument as is in this section mentioned, the benefit or burden of which runs with the reversion or the term.
This section applies where the covenant, agreement or condition is contained in any instrument—
creating a term of years absolute, or
varying the rights of the lessor or lessee under the instrument creating the term.