Update:
After getting our solicitors to talk it turns out that I was right not to pay rent while the building was burned down. The lease states that the rent will go on hold until the building is usable for the purpose it was leased.
As far as the ramps go, both solicitors agreed that it was the landlords responsibility to replace them as they were originally provided as part of the lease, and his failure to do so meant he was in breach of contract and the lease would be voided.
So while i'm glad that I don't owe him any money, and we have agreed that I can walk away, i'm still left with no business and no job.
Thanks for the advice/comments.