There is provision in law for the utility companies to force their equipment to be placed placed on private land without the agreement of the landowner.
This is only the case if the need is deemed for the general public good and there is no reasonable alternative place or route.
If the utility company wishes to go down the legal route they start by issuing a statutory notice to the landowner informing them of their intentions and giving them x months notice. The next stage is where the landowner takes the matter to court as provided for in the utility acts to object...and off they go down the legal route.
I live on a private road in an area with lots of private roads which are all private land so this one is seen every now and then.
Some seem to go down the statutory route with no discussion from the outset.
One found the landowner so intractable that they decided it was going to be cheaper overall to suddenly find an alternative route.
Another dispute is in progress and wayleave discussions have come to nothing with the company saying it has to be there, the landowner pointing out alternatives. I think the utility has offered a few hundred £ one off payment for the wayleave being granted which to the multi-millionaire owner was just a sick joke.
Where the landowner is large it always gets messy as land agents will be involved, solicitors will need to OK the documents etc. The problem is often not whether the current owner is bothered but whether a future owner might be.
An existing duct on private land will have a wayleave in place even if the details have been lost in time and probably never recorded anyway. BT probbaly knocked on owner's door 50 years ago asked if it would be OK, owner said yes provided they make good afterward and that was that - wayleave granted!
Where public lands ends and where private land starts particular on wide rural verges is another messy one. Generally the council claim public ownership at least for the first meter out from the tarmac (a footpath's width) but beyond that is down to individual cases, land documents etc.