Regarding direct routes over the sea to the east of the UK mainland, if you have filed to remain in CAS, the onus is very much on YOU to ask us what service we could provide below FL245/195.
Subject to workload in what can involve 2 or 3 Scottish sectors and the airfield, you will invariably get the route but NOT always a deconfliction service.
If you want to FILE direct then do so, but please take into account that we MAY limit UK FIS services and kindly do not forget to plan AROUND active Danger Areas and MDAs.
You would be amazed at the number of requests we get for directs through active MDAs, I wonder if anyone reads EN ROUTE Notams.
There are NO level restrictions into Newcastle or Durham from Scottish airspace AT ALL.
As my neighbour, 10W says, the FL260 restrictions at MARGO/NATEB for Scottish TMA airfields, FOYLE for EGPE and GRICE for EGPD are there for very good reasons.
They are roughly where 3 sectors meet, so to avoid having to co-ordinate ALL descents we have an agreed level procedure.
ALL of the FL260 restrictions ARE relaxed when traffic permits.