I may be a bit out of date here given that I stopped working at Edinburgh over a year ago and I'm not privy to airspace changes since then, but the issues are there...
All controlled airspace in the Scottish TMA above 6,000 ft belongs to Scottish Control, but in practice arriving IFR aircraft and IFR overflights which may conflict with them are transferred to Edinburgh or Glasgow Radar as appropriate when within 40 miles of PH/PF. For a start, the approach radar units can apply 3 mile lateral separation instead of 5 miles, and it's the approach radar units who have to sequence the arrivals onto final approach.
In general, VFR aircraft are not vectored or given a hard altitude assignment in the UK. That makes them an unknown quantity when mixing with IFR traffic. To have a sequence of inbound IFR traffic descending through a VFR at FL85 would be Hell on Earth when busy. That you'd have to get a clearance from Scottish but be transitting an area where the arriving traffic is controlled by Edinburgh would really makes things messy.
So, keep it simple. If you want the protection of controlled airspace and you're flying at FL85 (no doubt using GPS), pay the damn route charges and file IFR. If you don't want to, or can't file IFR, stay the **** out of the way of the people who are paying for a service.