Does an assembly of CE Marked sub-assemblies make for a compliant product?

Not necessarily. There are sound technical reasons why this should be so. The final manufacturer takes responsibility for the EMC performance of the completed product. Does the signatory of the Declaration of Conformity go to jail if the product is shown to be non-compliant? Not all offences under the UK Regulations could result in custodial penalties. Only Regulations 83 (contravention of a prohibition or suspension notice), 84 (giving false or misleading information) and 86(2) (impersonating an officer of an enforcement authority) have this penalty. To date, no-one has been sent to jail in the UK for infringement of a New Approach directive. It is possible that this could happen at some time in the future for a very serious breach of regulations, but this is complex issue of employment law, and is beyond the scope of these answers. Regulation 89 provides further information.