Thanks for input.
So, presuming I have found the right dead woman and ordered the right probate, that should give me helpful detail in 10 days or so.
From advice/info from various sources today:
Whoever is now responsible for the property had a duty to inform the land reg, which they have failed to do, maybe for 16 years! If this was solicitors it is a serious breach which they could be struck off for. One opinion was that by failing to register title, the new owners (whoever they are) have effectively forfeited the protections of the party wall act, so frankly, fuck em - although I'm not sure I'm brave enough to be that cavalier. The new owners are also presumably not paying ground rent or service charges to the freeholder, since he doesn't know who they are.
We can attempt to serve a party wall notice. However, once we do this, IF we don't get a response it automatically is in dispute. We then must appoint a surveyor who the tenant has to give access to. The surveyor will find in our favour but the upshot is we will have to spend £2k+ on some unnecessary paperwork.
The current tenant (whatever his standing - maybe he is the beneficiary, but if so, legally he isn't registered on the title) tried to sell the property in 2012, but the sale didn't complete - I deduced this from the estate agent who handled the listing. Not surprising given the lease is only 65 years so unmortgageable. How can he try to sell it if he isn't the registered owner?
Someone - the executor, the beneficiary - has to be the legal owner, right? It appears to be in some sort of limbo currently. This is what made me wonder - if a potential beneficiary had no way of paying the inheritance tax, could they prevaricate indefinitely on taking ownership? Particularly if they got the benefit anyway of a long-term free tenancy in the bargain??
One way or another, whoever is the legal owner of the leasehold has dodged some responsibilities for some years...
However, I'm unclear how I should handle it. By pushing for clear ownership details we are possibly opening a legal can of worms that our hermit NDN has been trying to avoid....but we need his cooperation really!