Could be Scab, a fungal disease that seems to particularly like Conference.

Spray regularly with a fungicide containing Myclobutanil or Mancozeb. Prune out any severely effected shoots and make sure that all leaves are raked up in autumn. Leave none on the ground below the tree.

cheers for that, will give it a try.

Probably should elaborate on the pruning bit. Canker which causes blackened shoot tips and splits on stems is best treated by pruning out effected stems (disinfect secateurs between each pruning too, especially between trees). Scab needs no pruning, just the spraying of leaves from bud burst until July every two weeks and the leaf clearance from around the base in autumn.