The problem with the old Wylex:-
1) Only rated 60 amps

2) Most were damaged over 30 amp fuse used.

3)

Those with the ability to take a larger fuse, it was only on the first fuse carrier. There was nothing to stop an ELCB-v from being fitted,

but the test gear

is long gone. But nothing to stop the ELCB-v from being replaced with an ELCB-c, but when that was done, it was often the 100 mA version. I have seen where the 100 mA has been swapped to 30 mA, and also seen the problem with it tripping all the time.
I remember having to call into the county council housing department, and while there hearing the calls for faults. Toilet leaking water out of the overflow for example, and thinking I would have simply adjusted the ball cock, and would have not dreamed of calling out a plumber. And I know in my mother's house, there was no way she could get her wheelchair under the stairs to reset a RCD, so a simply RCD trip was a call-out job. She did not call anyone out, it was automatic with the telecare, they would call me, and tell me the power had failed.
I can see why a Landlord would not want to be called out to reset a RCD, however, also saw what my mother did, when she found an extension lead with a flickering neon, with macular degeneration plus Alzheimer's disease, she did what in some ways seems sensible, she put the extension in a bucket of water, a wake-up call for me, and new consumer unit, in fact a re-wire was then done ASAP. But not easy, as could not really have it done with her in the house, and back then looking at £600 a week for accommodation for someone with Alzheimer's, and she had not been sectioned, so not permitted to lock her in. Lucky for an unrelated problem, the social services put her in a home for a time, so it was a mad dash to find someone who could rewire the house while she was away.
We all tend to look at our own homes, and forget some homes have children, and some have old people, and these may be visitors rather than the tenants, and with carers, they are at work, so HSE rules also kick in. Also seen this with the working from home, one is then at work, and all the HSE rules apply.
As to what insurance companies will allow, I don't know? But there are so many things which I can do at home, but not allowed to do when volunteering at a local heritage railway.
Before mother died, I looked at renting out her house to pay in part for her care, and putting her in a home, not what I wanted to do, but needed to be ready, and the letting agent came in, and it was a massive list of what needed to be done, seems the domino hob was not permitted, needed 4 heat areas, so when she died, I took easy way out and sold the house.
And I have seen it here, where landlords are simply selling up, too many hoops to jump through, seems there are caravan parks popping up everywhere, to fill the gap, and I do look at old two up and two down houses, and think even if not to spec, it would be better than a caravan!
But we don't make the rules, so we either pay up and get it to comply, or sell up, no real option to do anything else.