An I thought this house was bad, I had a home buyers report done, it pointed out a redundant fuse box was wedged between false ceiling and original ceiling, but it was not redundant. I had a fuse box and a consumer unit.
I has a new consumer unit fitted all RCBO's with idea any faults I can isolate that circuit, only fault found was a borrowed neutral on lights.
Getting the previous owner to have an EICR done, it seems
does not help read this link the electrician was taken to court and fined for not doing a proper job, but that does not help the new owner, his contract was with old owner.
My mothers house had a part rewire before being sold, kitchen and wet room already done, seem to remember around £3000 in 2017 approx, I did all the plastering, minimum done, with idea may need to rent it to pay for her care home, but she died so house sold.
But 1966 was the date when lights had to have an earth, so any house wired before 1966 one expects it will need a rewire. Post 1966 there were some problems with Ian Smith so some aluminium cable used, and also some cable poorly made and the plasticizer leached out, but one would be unlucky to find either, there was still some VIR cable used in early 60's, but by the 1970's we had gone metric, and so easy to see in the fuse box/consumer unit if cables imperial or metric. We have been metric now for over 50 years.
I tried to add RCD protection to my parents old house before the rewire, it did not work, if I could have got a 100 mA type S may have got away with it, but one RCD up front is not really a good idea.
Son fitted a new CU and lived in a caravan supplied from it while re-wiring, and slowly got more and more wired in, took around a year before they could move back into the house, I think he went OTT with things like server in the loft, but the only problem was the 16 amp supply did caravan and washing machine, and it was not enough for both, only thing used in house was washing machine.
I could have lived in the garage here had the house electrics not been up to scratch, except in may case not the electrics which was a nightmare, but leaking garage roof. Not short of cash, one expects problems with an old house, which need correcting, but getting tradesmen was the problem. As least one who when he did the roof, it actually stopped leaking.