asked the President of the Board of Trade in what imported articles it is usual to require a certificate that they are produced by workers earning trade union rates of wages?

No such certificates are required on the importation of any articles into this country.

Is not any sort of certificate required in the case of imported doors?

Not to my knowledge. It may be that the hon. and gallant Member is referring to what may be required under Clauses in the Fair Wages Clauses Act. According to the information at my disposal, no certificate of this kind is required in the case of any goods reaching this country.