1.) Yes

2.) Effectively they became mandatory at Euro V level-although a lot of Euro IV cars were fitted with them as guinea pigs to give the OEMs time to tune out any bugs before they became effectively compulsory.

Thanks at what years did Euro IV come into force?

Euro 4 became mandatory 01 January 2006 and ran to 31 December 2010, Euro 5 became mandatory on 01 January 2011. It was possible to buy Euro 4 cars prior to Jan 2006 just as it was possible to buy Euro 5 cars prior to Jan 2011. Back in Decemeber 2005 we bought a Euro 3 Focus with a huge discount, the delaers had either to sell the stock cars or pre-register them before the end of December, it was a great time to deal. In theory any Euro 3 cars not registered before 310 Decc 2005 should have been scrapped, wonder if that actually happened.