Yes, from the 1st July 2013, all UPVC windows fitted in the UK should have a CE Mark or certificate of proof.
The CE (conformité européenne) Mark indicates that goods meet the required safety standards set out by the European Union and can be sold in the EEA (European Economic Area). The CE Mark was introduced as part of harmonisation of product standards across the EU and is an important signal for consumers that those products have been manufactured correctly and meet safety standards.
The CE mark applies across many different types of home improvement products including windows and doors and must be displayed on the products by the manufacturer.
Since its introduction, the CE Mark has been used across the EU for many different types of product and become a signal that provides consumer confidence.