thundercat, to answer your question, well, the MOT tester currently does a smoke test, not an emission test (as such). There is no reason on these cars to worry about emissions as long as your car is not visibly smoking and is running correctly without hesitation or power problems. Yes you can clean the MAF if you want to but only if your having any of the problems I've mentioned.
If not, then leave well alone. Apart from as you say, a filter change and possibly a fuel filter change ( which should be mandatory if it's serviced regularly ) there's nothing else emissions wise you can do. I have in the past when I had a 25 TDI, took it out for a good revving boot session down the bypass before an MOT and cleared a lot of soot!!. But the L series is a completely different animal to the M47R lump so don't worry and good luck.
Regards DaDragon (roger)