I haven't looked at the route but my advice is to start with a straight line then deviate to avoid class A CAS, and go as high as you can. Surprisingly there are places even fairly close to London that you can go as high as 5500'. If crossing class D airspace, try and route from a VRP to VRP and at 90 deg to the runway if possible and if they refuse the transit request tell them you'll take an alternative routing. If they still refuse then have a plan to avoid the airspace.
I wouldn't necessarily avoid routing overhead airfields, especially if much higher, unless you know that there may be aero's overhead. Often though the aerobatics may take place a few miles away from the airfield so as not to upset the neighbours, so you could argue that overhead can be the safest place.