I think it is binding on them, subject to a review of the lease and its wording.
One option is to say its binding, take it up with former landlord and he was obligated to declare it, not me, and by all means take it to the LVT for determination if you wish.
In the meantine here is the document and my notice fee of £25 ( less if the lease says so or nothing if it doesnt require a fee to be paid)
Based on the information posted, I offer my thoughts.Any action you then take is your liability. While commending individual effort, there is no substitute for a thorough review of documents and facts by paid for professional advisers. More ramblings atleaseholdpropertymanager.blogspot.com