OK, OK...lets get this right... The RN don't have their own rules...the rules are as stated in the MILAIP which is an unclassified document and so here goes...
Inside Controlled airspace they must maintain 1500m Horizontal, 1000' Vertical OR COCISOS. (Only if they are doing less than 140 knots - merlin gods have different rules if they are going fast)
The 1500 m rule can be reduced if they manoeuvre at a speed so that they can have adequate opportunity to avoid other traffic or obstacles and avoid a collision.
Outside CAS the rules are the same provided you are below 3000' amsl. above that and the COCISOS rule isn't valid.
Below 2000'agl there are different rules again.
Im 99% certain thats it but may have missed something out...help anyone?
If it was an RN Sea King(Grey and red) then it was almost certainly on a job as there is no other reason for it to be in or around Dundee... a long way from its base....where was the Lossie cab?