asked the Postmaster-General what restrictions he places on the use of official paid envelopes by nationalised undertakings and associated companies for their ordinary postal correspondence; what steps are taken by his Department to verify the suitability of a firm to make use of postal services at the public expense; and, in particular, if the National Screen Service, Ltd., comes under the heading of a nationalised or an associated company which is entitled by his regulations to use official paid postal service for the distribution of their films.