OK lets get some facts in here.
First of all, the UK operates a Joint and integrated ATC policy for the benefit of all users. If a route is outside CAS then in the London FIR, the military can provide a service, if a military jet wants to fly GAT, then he does. On the subject of the North Sea route, comments above about D323 are quite correct. However, there are vast tracts of the day when the D323 complex is NOT active and the routes through it, UM981/982 UM90 and I think the other one is UM91 become CDR3s. A CDR 3 can be used tactically. This means that you can fly along the CDR that goes to Newcastle.
This is when it gets a bit difficult. The boundary between the Scottish and London ATC sectors goes along the north of Y70. If you go to OTR, you remain with LACC and get transferred to LATCC Mil at about FL260 northbound. If you use the CDR, this is in SCACC airspace and they will of course not know about you because you have not flight-planned that route. So chucking you at ScACC civil for that portion of the route is a no go really.
The option is to work London Mil for that portion, as you will be going to them anyway at OTR. There are a number of ways this can happen. Either the civil controller can offer you at the FIR boundary to London Mil (either on their own volition or on request from you) or the Supervisor at London Mil can be proactive and suggest this to the LAS at LACC.
It does depend on the workload of LATCC Mil but as you will be in the upper air, you are a high priority and as I said before, they will be working you anyway. Benefits for the Mil controller are, He/she will get rid of you much earlier, he/she can avoid the Vale of York both laterally and vertically because you can stay higher for longer (not required to be level FL260 by OTR) Benefits for you are obviously time , fuel and carbon.
To know when the CDRs are available you will need to look at the CRAM (conditional route availability message) this is published by 1500 the day before so you can see if D323 is active or not and therefore know if your request is likely to be refused.
There is no such thing as Military or Civil airspace. "it is to be one continuum and used flexibly on a day to day basis" A one way street sometimes but, you are entitled to the short cut as long as it is a recognised route, which these are. It saves money and is safer for all concerned rather than descending through the Vale of York.
Cheersnow!
