> It is not always known where those massive pipes are through the land
These pipelines are quite easily identified on-shore by surface markers in the UK[0]. Also, like I did, folks would have noticed the fairly substantial earthworks that went on when they were being installed....and bided their time if they were to interfere with them. I remember the excavations in Scotland for these pipelines back in the late 70's and 80's. There's no big secret about them.
As to offshore, well your "terrorists" are going to need a fairly huge amount of resources to attack them...deep sea divers, vessels large enough to withstand North Sea storms etc.
I have read an account of the SBS storming a North Sea rig as part of an exercise and it wasn't exactly easy for them with all the very best training and gear and supported by Royal Navy ships - and that was in reasonable weather conditions.
These pipelines are quite easily identified on-shore by surface markers in the UK[0]. Also, like I did, folks would have noticed the fairly substantial earthworks that went on when they were being installed....and bided their time if they were to interfere with them. I remember the excavations in Scotland for these pipelines back in the late 70's and 80's. There's no big secret about them.
As to offshore, well your "terrorists" are going to need a fairly huge amount of resources to attack them...deep sea divers, vessels large enough to withstand North Sea storms etc.
[0]: https://www.alamy.com/stock-photo-oil-pipeline-marker-with-f...