There’s much more to buying a helmet than choosing the colour or style that you like! Firstly the helmet must meet UNECE Regulation 22.05 standards. We strongly recommend that you never purchase a second hand helmet or order from a website. You must try on a few helmets from different manufacturers to find what fits you best.
The UK Government launched the SHARP Helmet Safety Scheme website where you can see the safety ratings for helmets as well as great advice.