Hello I am a solicitor with 20 years experience. I will try to answer this for you.
I don't see what claim he has. He bought a property with a Rent Act Protected tenant, which he had no right to get of and she leaves conveniently for him thereby handing him a massive windfall. I find it incredible he has the cheek to complain about everything. Has she actually actually left permanently or does she intend to return if she gets better? A protected tenancy is not something to give up lightly.
Your mother would have a legal right to get he landlord to fix those structure/exterior repairs and to compensate her if he didn't.
Assuming that your mother didn't damage the property after he bought it then caveat emptor applies and he takes the place as it is.
He is a chancer trying to exploit a vulnerable old lady.
I am sorry. I thought I had answered this morning but that reply seems to have got lost somewhere.
He is responsible for structural disrepair/exterior disrepair inc windows from the moment he has notice of the
disrepair plus a reasonable amount of time. Your mother may have a claim against him.
When did he get the property?
I have never heard of tenants assurance guarantee. I specialise in landlord and tenant law, none of my colleagues have heard of it either.
You should take photos of the property when you go round to protect your position.
His claim is likely to be without merit and is probably just an attempt to exploit your mother.