psmk2, good evening
Is there a lease agreement as to who will be responsible for repairs of various types?
Some Commercial agreements make the Tennant, the Commercial operator Liable for repairs to the building, others do not, check the leasing agreement
As for the "Tenement Act Scotland" this refers to the actual owner of the Property, NOT the tenant!
So find your lease and read it??
If you "own" the cellar and are leasing the Shop then unless the lease confirms that the Shop owner is in some way Liable, you may? have to fund the repair + possibly a claim for loss of profit from the Commercial property? it comes down to the Lease agreement
As for an Insurance claim, really sorry here but there are specific exclusions in almost all Insurance policies as regards wood boring insects, again you will need to have a look at your policy Wording [Fine print gets you in the end]
Sorry to be the bearer of bad tidings, but I see this sort of situation regularly when I deal with Insurance claims.
As for "Serving a Notice" no such provision in Scotland, sorry about that.
Ken.