What the notice actually is
Section 20 of the Landlord and Tenant Act 1985 requires a landlord to consult leaseholders before carrying out major works, and limits what can be recovered from each leaseholder if the consultation is not carried out properly. It is a protection, not a bill.
The consultation runs in stages: notice of intention, then estimates, then notice of the award. The practical effect for a buyer is that a notice which has only been anticipated carries no number at all, and a notice at the estimates stage carries a number that may still move.