Thanks all for the advice. One thing which is missing, be it K&N, Pipercross or ITG is the part number!
I've checked with Pipercross, the nearest fitting, PX229 I think, is for the M16 and they wont confirm it's OK for the T16 although the airbox looks identical.
Brian I still have the K&N box in the garage. It has E-2360 on it.
I have also the standard filter it replaced which has c 500 miles of use if anyone wants it.