Hehehe. I fear 500 miles maybe a fantasy, but driving carefully could return 30-32 mpg without too much difficulty.
Just did my tyre pressures. Offside front 38, Offside rear 41, nearside front and rear I couldn't see, but I had the macjine set to 34 and both front and rear required air. At a rough guess I think the rear could've been near 25. Slow puncture pressure I think. Anyway, now all tyres are at 34 psi and I'll keep a closer eye on this to ensure there aren't any other issues.
Stuart