repairs / dilapidations

i took over a pub back in may of last year on a new 20 year lease (no assignment,, just purchased outgoing tenants f&f). In november we started a scheme of work in alliance with the pubco, but midway through we found that two first floor fireplaces were unsupported and in danger of collapse down into the ground floor trading area. Before work could continue on our planned scheme of work steelwork had to be put in to support the two fireplaces. The decision to do this was taken jointly with the pubco, as there seemed no alternative - once we knew the problem was there we couldn't have customers drinking underneath. It seems to me from reading my lease and a bit of internet research that i have no liability for any work which goes beyond repairing back to the state that the building was in before our lease began (even if nobody knew exactly what that state was at the time), but the pubco seems to think otherwise. This opens up a while can of worms, as this is a victorian building which was knocked about after the war, if the building ever needs repair due to previously substandard work then the insurance company will not pay out - leaving me with the liability (or so the pubco claims).

I would have thought that there would be a clear line between work which is a "repair" and work to correct structural problems which pre-date the lease. Has anyone any experience of a similar situation? I am keen to do as much research myself before seeking expensive legal / surveyors advice, in the hope that if I can make a good case the pubco will backdown and agree to make at least a substantial contribution towards the cost of the steelwork.

I would have thought that the same principle would apply whenever a leaseholder found a problem with a building which predates the lease, but is significant enough to prevent the building being used for its "intended use" (a pub). Can the pubco really demand that the leaseholder foots the bill? Or is there an impplied obligation on the freeholder to provide a building which is structurally sound? tom Bailey