thank you. There are a couple of approaches you can look at in terms of potentially challenging the notice that has been served upon you.
If you can show that the freeholder has failed to properly attend to its repairing obligations in the past for which you may require a surveyor's report which you may need to obtain either on your own initiative or jointly with one or more other residents in order to share costs, then you can make a claim against the landlord for breach of their lease obligations to keep in good repair the common elements and structure of the property.
Damages in this regard are calculated by reference to a notional market rent for the property. In addition, as a result of the decision in Simmons v Castle EWCA Civ 1288 you can also seek an additional 10% uplift on the above figure.
If you decide to issue proceedings against the landlord on the above basis, you can consider issuing proceedings under part eight of the civil procedure rules which deals with disputes in which there is no substantive dispute as regards fact:
https://www.gov.uk/government/publications/form-n208-claim-form-cpr-part-8
alternatively, the following form if there is likely to be substantive dispute as regards facts:
https://www.gov.uk/government/publications/form-n1-claim-form-cpr-part-7
if there is no substantive claim of failure to maintain on the part of the landlord but these are simply repairs that have become necessary due to the passing of time and general wear and tear that has occurred to the property over that period, then the above may not be possible but you may still be able to challenge the reasonableness of the amount that is being proposed in terms of the money being due. If for example the landlord is ignoring a cheaper alternative than the works proposed always using a contractor which is unduly costly as compared to other contractors.
if this is an approach you wish to consider, then in the first instance, you can raise concerns with the landlord and ultimately, you can bring an application to the first tier property tribunal to determine the reasonableness of the amounts proposed using the following form:
https://www.gov.uk/government/publications/form-leasehold-3-application-for-a-determination-of-liability-to-pay-and-reasonableness-of-service-charges