A conveyance of the freehold or grant of a lease in pursuance of this Part shall contain (unless, in the case of a conveyance or grant in pursuance of the right to buy, there is no discount) a covenant binding on the secure tenant and his successors in title to the following effect.
In the case of a conveyance or grant in pursuance of the right to buy, the covenant shall be to pay the landlord such sum (if any) as the landlord may demand in accordance with section 155A on the occasion of the first relevant disposal (other than an exempted disposal) which takes place within the period of five years beginning with the conveyance or grant.
In the case of a conveyance or grant in pursuance of the right to acquire on rent to mortgage terms, the covenant shall be to pay the landlord such sum (if any) as the landlord may demand in accordance with section 155B on the occasion of the first relevant disposal (other than an exempted disposal) which takes place within the period of five years beginning with the making of the initial payment.
Where a secure tenant has served on his landlord an operative notice of delay, as defined in section 153A,—