does anyone know of a belt you can use to remove the alternator on a 300 tdi defender and put it where people usually put the second alternator as I need the room where the alternator is at the moment and just want to move it to the other side but need a longer belt.

You should be able to work it out for yourself, serpentine belts are normally marked something like 7PK1500. The 7PK bit is the number of peaks the belt has (7) so that shouldn't change from what you have (assuming its 7 obviously), the 1500 is the belt length in mm's. If you can mount the alternator where you want it you should be able to work out the belt length with some non elastic cord mimicking the new belt run. Don't forget to take the tensioner into consideration (unless you are doing that by moving the alternator). Once you have worked out your new belt length do a search for it (i.e. 7PK1350). Think belt length is normally in 5mm steps so you may have to experiment a bit with the search.

Nice one mate thats the route I was going down just wondered if anyone had done it and new the part no of said belt cheers.

And they are fraction of the normal price if you buy them direct from Gates.