Changes to Council Directive 1999/37/EC of 29 April 1999 on the registration documents for vehicles
EU Directive 1999/37
Made by Council Directive 2013/22/EU of 13 May 2013 adapting certain directives in the field of transport policy, by reason of the accession of the Republic of Croatia
From legislation.gov.uk's record of changes, the official one: see it there.