European pipe is standardized to 
ISO 2531 and its descendent specifications EN 545 (potable water) and EN 598 (sewage).  European pipes are sized to approximately match the internal diameter of the pipe, following internal lining, to the nominal diameter.  ISO 2531 maintains dimensional compatibility with older German cast iron pipes.  Older British pipes, however, which used the incompatible imperial standard, BS 78, require adapter pieces when connecting to newly installed pipe.  Coincidentally, the British harmonization with European pipe standards occurred at approximately the same time as its transition to ductile iron, so almost all cast iron pipe is imperial and all ductile pipe is metric.
Other European Standards give specifications on more dedicated products:
EN 15655:2009 – Ductile iron pipes, fittings and accessories – Internal polyurethane lining for pipes and fittings – Requirements and test methods
EN 877:1999/A1:2006 – Cast iron pipes and fittings, their joints and accessories for the evacuation of water from buildings – Requirements, test methods and quality assurance
CEN/TR 15545:2006 – Guide to the use of EN 545
CEN/TR 16017:2010 – Guide to the use of EN 598
EN 877:1999 – Cast iron pipes and fittings, their joints and accessories for the evacuation of water from buildings – Requirements, test methods and quality assurance
EN 877:1999/A1:2006/AC:2008 – Cast iron pipes and fittings, their joints and accessories for the evacuation of water from buildings – Requirements, test methods and quality assurance
EN 598:2007+A1:2009 – Ductile iron pipes, fittings, accessories and their joints for sewerage applications – Requirements and test methods
EN 12842:2012 – Ductile iron fittings for PVC-U or PE piping systems – Requirements and test methods
CEN/TR 16470:2013 – Environmental aspects of ductile iron pipe systems for water and sewerage applications
EN 14628:2005 – Ductile iron pipes, fittings and accessories – External polyethylene coating for pipes – Requirements and test methods
EN 15189:2006 – Ductile iron pipes, fittings and accessories – External polyurethane coating for pipes – Requirements and test methods
EN 14901:2014 – Ductile iron pipes, fittings and accessories – Epoxy coating (heavy duty) of ductile iron fittings and accessories – Requirements and test methods
EN 969:2009 – Ductile iron pipes, fittings, accessories and their joints for gas pipelines – Requirements and test methods
EN 15542:2008 – Ductile iron pipes, fittings and accessories – External cement mortar coating for pipes – Requirements and test methods
EN 545:2010 – Ductile iron pipes, fittings, accessories and their joints for water pipelines – Requirements and test methods
EN 14525:2004 – Ductile iron wide tolerance couplings and flange adaptors for use with pipes of different materials: ductile iron, Grey iron, Steel, PVC-U PE, Fibre-cement