I had a very similar situation with SPEN with a transformer pole on my boundary (supplying a 3rd party, no benefit to me).
There was no wayleave or easement in place - I’d applied to the network operator when we first moved in and had all of their paperwork sat awaiting my signature, but had left it ‘open’ and never sent anything back. They had clearly agreed that the apparatus was on my land though.
Fast forward a couple of years and I’d been in discussions with them about getting the pole moved and a new connection for me from it to feed a new shed. Things moved glacially so we ended up erecting the steel frame (it was about 1.5m from the 11Kv conductors) and got them out for a site meeting.
They insisted that we stopped working on the building, I suggested (politely) that they remove their apparatus off my land ASAP, things moved up a few gears and they shifted the pole and sorted my new connection soon-after.
It’s definitely worth keeping everything polite and amicable, but very important to set out your stall early on, don’t get bulldozed into submission by them, don’t accept ‘Computer says no’, and realise you are holding a decent trump card if their apparatus is on your land without any formal agreement in place.
