I know how to get rid of it!
Ok here goes people! the solution!
It is a mission but it did solve it for me until i took the covers off again
haha
So take the cover off the back and attach one of those little silica bag things you get in the box with new trainers, i just stuck it on with a bit of tape but didnt cover it completely with tape as i guessed the tape would stop the moisture being sucked in.
Replace cover and leave in for a day or two using the headlights as much as possible.
Wait for it not to be raining (never in this country)
Remove silica bag from cover and replace cover with a little vasoline or greese or something round the edge to make sure its a good seal.
I did this and it didnt fog up at all for maybe a month until i had to replace a headlight bulb so did them both with some nice uprated ones, now ive put the covers back on they are steaming up again
The only thing is that to do it properly without cutting your hands to shreds and swearing alot you have to remove the whole light unit and that means bumper off
Disclaimer
This worked for me! if you try it and mess it up dont come crying to me haha