6. No growing crop certificate may be issued containing a statement that seed potatoes are capable of being marketed as pre-basic seed potatoes of Union grade PB unless the authorised officer is satisfied that the immediately succeeding crop produced from the seed potatoes is not likely to contain—U.K.
(a)more than 0.01% by number of growing plants which deviate from variety and type or are a different variety; or
(b)more than 0.5% by number of growing plants which show symptoms of virus diseases where those symptoms are attributable to infection in the mother crop.