With contract manufacturing, who is responsible for the Declaration of Conformity?

This should be a contractual matter to be agreed between customer and supplier. The authorities in the UK seem to have a relaxed attitude about who issues the Declaration of Conformity providing the declaration is produced. Guidance from the Commission suggests that a manufacturer may subcontract design or production providing he retains overall control and responsibility for the apparatus as a whole. Logically, the organization taking responsibility for the design and performance of the product should be responsible, but they will need to demonstrate (via Quality Management Systems or otherwise) that they have control over the manufacturing process as if the they were manufacturing the product themselves.