Job done, looks brilliant. What a cheap and worthwhile fix!
For anyone who'se interested:
1. Removed grill and battery cover.
2. Wiggled off the sidelamps
3. Removed headlamps - you have to disconnect the washer fluid line to the headlamp washers.
4. Removed washer wipers, bit of trim and washer motors
5. Took out all the bulbs AND the high beam bulb holder (small allen key)
6. Had a go with compressed air (low pressure) through the bulb holders and all around generally.
7. Coughed a lot in a great cloud of dust. Repeated with other headlamp.
8. Got a couple of bottle brushes (thanks Gav), some jiffy cloth and some white spirit.
9. Wrapped a brush tightly in jiffy cloth, held with lots of string wrapped around it.
10. Swabbed around the inside to pick up the dust loosened by the air.
11. Poured in about 20 - 30 ml of white spirit and sloshed it around the inside of the lens. You can’t really slosh it around the reflectors cos it'll all pour out.
12. This bit is important, tilted the assembly so all the liquid came to one side carrying whatever dirt was in it. So when it evaporates, the dirt is now in one place.
13. Allow to evaporate.
14. Jiffy swab again, gently and painstakingly. Got a TON of grime out. Use the bendy bottle brush to maximum effect. Put it through both holders for better reach (beam and beam/dipped).
15. Snipped a hole in the jiffy so a few bristles could poke out, better to clean the grooves inside the lenses.
16. Reassemble.
17. Read the tip about getting the MOT chaps to do the alignment (cheers Basher). Remembered they generally do that for free during the MOT anyway so used neighbours wall to "more or less" adjust the beams by hand. They were both high and one was wide.
18. Done. Three hours. Not only good night visibility but car looks spanking too!