I bagged a set of 16" wheels from a 2004 Freebie and wrongly assumed they would fit my 2002 TD4 (currently with 15"). Unfortunately the rear wheels foul on the brake drums - but not by much. Is it feasible to use some 5mm spacers to get the clearance back?

The rims you have got can not be from a 2004 as they would be the bigger ones as they changed in 2002 from your year so any rims 2002 onwards would fit yours its prior 2002 that would not. Maybe the rims you have bought were not the original ones on the 2004

I am slowly coming to the same conclusion as the TD4 got the bigger rear brakes like the V6 didn't it?. In which case these 16" wheels must be from an earlier model.

I stuck an old 5mm spacer behind one today as a test (before it poured down with rain) It seems to (only just) clear the drum now and still have a connection with the hub spigot and also have 9 turns on the wheel nuts ..... so looking good so far.

I wonder if the fronts will have any surprises for me - there looks as though there should be bags of room between wheel and caliper