I'm no expert on this matter so don't rely on this info, but your management company's reply seems very suspect:
The management company for the estate has told me that this is not under the block policy as the leak is in my apartment
Do you have a lease/freehold on the apartment? If its a lease it would be my understanding that you only own the fittings (my insurer says this is anything that you can take with you, I imagine without resorting to a pneumatic hammer) in the apartment and the right to use the apartment (for the duration of the lease). Therefore any damage to the apartment IS the responsibility of the management company since they de facto own the apartment.
Obviously, the devil is in the detail, so you really need to check all the relevant documentation. Ask for a copy of the block insurance policy, the policy number, and contact details for the insurance company and/or broker. You are a shareholder of the management company so I'd imagine you are entitled to this information. Then contact the insurer/broker, they probably won't deal direct with you, my experience anyway, but just say all you want to know is if your covered.
If it turns out that you are not covered, and non of the assumptions I have made are incorrect, then it may be the case that the managment company didn't get adequate insurance cover. I have no idea of their legal obligations to provide this but your solicitor might know.
I am currently processing a claim via the block insurance policy due to a leak in my apartment so far I haven't had any problems.
Hope this helps.