Hi Dave, I'm glad you saw my post regarding brush painting before it got lost.
Airfix kits, as with many other manufacturers rehash old kits and so the moulds could end up being quite old. Some Airfix offerrings are better than others but that goes for Revell just as much. The latest 1/72 u-boat kits are superb but old 1/72nd Revell aircraft were not as crisp.
Unfortunately a lot of manufacturers go for raised panel lines, quite incorrectly, simply as they are cheaper to produce. If you want to really make the most of the model you should remove the raised lines and re-scribe new recessed panel lines but that is a lot of work and maybe more than you want to do. If you will have to do this anyway when you fill the fuselage then maybe it is worth thinking about.
As for applying washes to raised detail look at my own Revell U-boat build thread where you will see that is exactly what I have done there.
http://www.scale-models.co.uk/showthread.php?t=2410