No earth on his DNO TN-S supply, No earthing from an earth rod, No earthing from either the Water and Gas bonding connections to service pipes, ... And the OP can't even say this situation was present before he started any work.
Something is very wrong here. Have to wonder if the OP even checked bonding was in place, before starting this CU change!!
I have yet to see a broken down TN-S earthing supply with 0 ohms, that is almost an impossible scenario. Add to that, the bonding of service pipes (if not both plastic) not having any potential either, the chances then become astronomical of a L-E test being 0!! lol!!
If and it's a very big IF, the incoming TN-S had a really high or an impossible Ze value 0. then the very first thing you would do is call in the DNO as an emergency situation, not go ahead and do a CU change, ...find you have a problem, then start fluffing around installing an earth rod!!
I'll take some of that Oxygen now if there's any left!! lol!!