That implies that the others have got complete maps - which I find much more surprising. Every time that I have had any dealings with any utility companies - which I do as part of my job - it becomes apparent very early on that they don't have anything like accurate maps in whatever area I am looking at. And not just for old lines that they inherited - as seems to be the issue here - but for things like fibre optics that I saw them lay myself just 18 months earlier.
Several years ago I was working on water sites and they didn't even have accurate info about the stuff on their own sites. The head office staff thought they did though. Just the computers did not match reality. Running many of the sites was entirely reliant on the knowledge of site operators who were all about to retire. There was no younger staff being taught anything either.
I'm in the US and a few years back we had to replace our septic system.. Did all the usual stuff to contact utility companies to come mark the lines off.
The cable company we had has been bought out twice in my memory, who knows how many times before that. They marked a straight line from certain points around the front of the house.
Well guess who sliced through the cable with the very first excavator chunk out BACK.
The placement made no sense until you consider a tree that had been cut down and stump removed, on the close front side of the house vs the completely clear, easily dug up but farther to go back side. Looks to me like someone didn't want to deal with roots and too the easy way, but didn't change the reported line. I don't know how cable guys usually mark their lines but I thought it was weird he only had a clipboard and some measuring tape instead of like... A metal detector. Idk if the lines can even be picked up with one though.
Another time I noticed water visibly flowing underneath the house from front to back through the foundation bricks. NOT good. At all. Very bad, in fact, to have flowing water under your house.
Thanks to the grass growing extra tall, and the excessive amount of groundwater I was able to track down a leak to a little spurt of water maybe 3 inches high coming from the ground. Called the water company about a busted pipe.
Apparently they had two lines next to each other, one was a replacement and the other was supposed to be bypassed but apparently never got cut off. So when the old line eventually completely broke, it just started pouring water into the hillside which ran down to our house. Three crews working until about 5am. Water spraying a good 15 feet into the air.
So they new where the pipe was, but they didn't really know where the pipe was since their papers said the actual leaky pipe no longer existed.
Whenever groundwork is done you're supposed to apply for some kind of permit and part of that process is that they're supposed to tell you if there's any underground utilities.
I can't count the number of times though that our engineers have dug up a fiber line or something that we would demonstrably told was not there. It's great because sometimes you can see on the pavement that it's being dug up and resurfaced in a different material so there's obviously something down there, but the paperwork says, nope we just dug it up for no reason there's nothing down there go mad.
You don't apply for a permit, you go to LinesearchbeforeUdig - lsbud.co.uk. This is a free service anyone can use, and you'll get emails from various asset owners with maps of what they have in the area you select. Some might try to charge for this, these ones are assholes.
As far as the law is concerned, it's up to you to make sure you do it right and the costs for doing it wrong will all fall on your shoulders.
The only permit you need AFAIK is planning permission - which won't be granted until you convince them you've done a sufficient line search. Aside from that, you need permission from the land owner, of course.
One reason for this lack of mapping is due to the Water and Sewerage companies taking on the ownership of most private sewers, lateral drains and pumping stations. These were transferred into their ownership on the 01/10/2011, pumping stations changed ownership 01/10/2016.