6. Where the holder of the authorisation has been informed by the licensing authority that any batch of any investigational medicinal product to which his authorisation relates has been found not to conform as regards strength, quality or purity with—
(a)the specification of the relevant product; or
(b)the provisions of these Regulations, the Act or any regulations under the Act that are applicable to the investigational medicinal product,
he shall, if so directed, withhold such batch from distribution for use in clinical trials, so far as may be reasonably practicable, for such a period not exceeding six weeks as may be specified by the licensing authority.