Hi Nick,
Another trick is to apply surfactant to your glass. Sofactant is the world's greatest water repellent. It's the main constituent of those expensive anti-rain and anti-mist products like RainX, sold in Halfords and the like. IT'S ALSO THE MAIN CONSTITUENT OF FABRIC SOFTENERS that you put in your washing machine.
CAUTION - Never apply RainX or other surfactant to the outside of the front windshield of a Defender! Because the windscreen is flat upright, as versus most of today's cars' sloped windscreens, the airflow will create problems with pooling the raindrops, rather than blowing them away. It'll also cause your wipers to shudder.
DO, however, apply fabric conditioner to the inside of the windscreen, as well as to both the inside and outside of all other glass. This includes polishing the headlight glass and your mirrors.
Sofactant will stop misting on the inside glass. Sofactant, because it repels water, will also help keep the outside glass clean(er) than it'd otherwise be, because the moisture in dirty road spray can't stick to the glass so easily. That means the dirty road spray will partly wash your headlamps rather than just dimming them. It'll also reduce the notorious build up of muck on the rear door glass -- retaining some rear view -- by up to 30%. (But, as I say, Do NOT apply to the front windshield.)
You can also choose some very nice smelling fabric conditioners, as well as saving yourself a pretty penny.
Have fun,
Rick