Changes to Council Directive of 29 June 1990 concerning a Community procedure to improve the transparency of gas and electricity prices charged to industrial end-users (90/377/EEC)
EU Directive 1990/377
Made by Council Directive 2006/108/EC of 20 November 2006 adapting Directives 90/377/EEC and 2001/77/EC in the field of energy, by reason of the accession of Bulgaria and Romania
From legislation.gov.uk's record of changes, the official one: see it there.