no, the compound dries under soil/sealed its a 2 part resin.
everyones will possibly be in the same state, not 100% they will, the one in question has been nocked about big time
so houses are 1956 build, well, im currently on a job with a 1930s service cable, still fine
and, NO your earth does NOT rely on the armour tape, it relys on the lead sheath which is under the armour/bitumen/armour/bitumen layer
and aside from that, its effectivly a gigantic earth spike
plus, this is the reason for periodic testing
its also not mastic it looks like duct putty
either way its a bodge, the jointer must have been new or something or he had a dodgey shell to use, cos they usualy use tape because the gap is usualy only a few mm
also, writing a letter will get you nothing, they will give you a reply something along the lines of "thank you for the concern mr bas we do undertake inspection of our supply cables blah blah blah thank you for your intrest after a breif company policy and how they value your safety
its like this with EDF:
You have a problem, they will fix it
if its not causing a problem they wont
i phone em for cut out changes if the cutout is old cast iron, they come out within 2 weeks and jobs done for me, they even ask me to renew the tails between the cutout and meter with 25mm!!! i do it for a hastle free life!
even if i phoned em and said dont like the look of your joint mate.....nothing would be done....
if you want action call maintenance and say theres a joint at the end of your road and as you were walking past at 9 pm with doggy you saw smoke comming off the cable
then you might get somone within an hour, however, thats as far as it will go if its not smoking when he gets there
infact, i know of a case when a spark complained about the haigh earth reading on a tn-s they replaced a section of cable to the cutout and declaired it as a TT
recently, i asked for a cutout change, they came out 2 weeks later, dug a section of cable outside, through concrete drive to cut the cable so it was a dead cutout change, when they were digging they hit their own cable, went and sat in the van, manager came out, took a picture, they did the job and joined teh cable, next day decided concrete would take too long so re-enstated the concrete drive with tarmac....
did you also know that if an electricity pole is on your land without a wayleve they will enforce a retrospective order and get one which again leaves you the under dog
dont mean to sway off topic but you really are wasting your time
get an EFLI meter on your cutout and if its high complain it will be fixed, if its low, leave it, your in london i beleve so not likly to be more than 200 meters from a sub station