Is anyone here a surveyor?

it doesn't matter one bit.

you are a tenant/lessee with a contract with your landlord/freeholder. Presumably that contracts states right of use and access to communal parts. They have a duty to uphold their end of the bargain and as such **they **are liable.

You do not have a contract with nisa or the managing agent. The managing agent is in place to represent the freeholder as an agent. what he says represents the freeholder, but that doesn't mean that he has a duty to you.

My advice: do not go down the route of engaging a surveyor. You'll take on an implied liability by the act of investigating this. Get the landlord/freeholders solicitors details and get yourself a solicitor who can fax a letter over to them stating that you hold them liable for breach of contract and costs incurred if normal service isn't resumed pronto.

I spoke to the FD of the company that holds the freehold- he said that it was nothing to do with them as they pay the management company to manage the situation.

He said that as the freeholder he would do nothing, as it was not his responsibility.