Englishal, i can't belive if your flying at say 4000ft (TL 3000ft) you would use FL's or the quadrant rule for VFR flying!!. Also, changing to IFR flight rules if you happen to meet cloud is ok if your qualified, best way is if your VFR, stay VFR, or dont fly.
Why not? Why not fly at FL40 in that case, or 45, 50, 55, 60, 65, 70, 75, 80, etc.... for that matter if you can? if I was coming down across Wales I'd climb to FL75 rather than at 7500' I might even try FL195 VFR
FL will ensure you don't bust airspace as they will be marked in FL. How do you know, for example that 6500' Regional will keep you clear of the airway North of exeter which is FL65?
PS If you fly to France or go to the USA you HAVE to fly semi-circular rules when VFR (odd+500, even+500), no choice. So may as well get into the habit. It might also seperate you from IFR traffic.