Drum you will have to trim this for sure, assuming you are refering to your disco II (in this thread:
http://www.landroversonly.com/forums/showthread.php?t=5102)
I am running 265/75-16 BFG M/T's, to be able to turn my steering wheel I had to trim the inside fender guard-things to about half way up the bumper so it would clear them under full articulation and trim the lower edge of the bumper a bit, otherwise, there are no other modifications required.
As you can see in this last picture, the tire is forward a tad in the wheel well, that is why you have to do the trimming. Also note that on very tight cornering the tires will rub on the control arbs a bit, but there is nothing you can really do about it.
