Actually... i belive SOSUS atm has GPS recievers that are accessible by civilian structures too for maritime research. So.... yeah?
As i said already those subs are not used for cable-laying, at the best are used for observation of the cable state or some assistance during repair. Cables are layed by cable-laying ships, list of which we have, so if someone cared that much could check their deployments last few years and see where they were active.
They forced maritime patrol role from Nimrods onto C-130s for now and C3I onto Sentries for now till adequate replacement gets selected, but seems it will be role taken by P-8s we mentioned above.
UK is not trying to position itself as superpowere, Russa is. While tiny Japan triples your ASW/maritime patrol capabilities its sort of funny, but if its okay, sure, dont mind me i am just thinking loud.
So, basic geography:
Best part of the Russian coastline covered with ice during wither, and best part of the sea around Russia covered all year long as well.
So maritime patrol air-planes useless on the 30-80% of the sea , depending on season.
Means that example a poseidon P-8 useful only to hunt polar bears with the torpedoes and sonabouys. Maybe it can hit them on the head, and entertain the bored crew.
The only way to collect data about enemy submarines ( with say 120 tomahawk rocket) is to plant passive sonar onto the seabed.
By quick calculation Russia has 8 million sqkm EEZ , it needs something like 1000 passive sonar to cover ALL of this area.
The area needs no more than 80 000 km of cable ( way less actually, it is lazy and rough calculation)
The cable network is the most expensive part of the story, the sonars cant cost more than 3 billion $( actually one sonabuy cost less than 5000 $, so the 3 billion maybe a bit stretch by one magnitude) .
The cabling can't cost more than 8 billion, but is is maybe one magnitude more than the real cost.
It means the whole sensor network cost less than four helicopter carrier, and more capable, considering the helicopter carrier can't operate on ice.
Actually no ship/submarine can get close to the shores by more than 700 km.
All that the system needs is torpedo/rocket carrying platform , see bastion/kilo/nuc subs around arctic.
Additional information: it is pretty hard to use cable laying ship on the ice : p.
And actually you need a pair of hands to connect the sonars to the cabling.And the sonar cables needs directional laying at least perpendicularly from the data collector.