First of all you'll need to purchase a heating element for the radiator.
Go to your link above and follow the navigation to the section about elements.
It will be better to buy a dual fuel kit
http://towel-radiator.com/categories/Electric-Elements/Dual-Fuel-Heated-Towel-Rails/
Providing electrical stuff in bathrooms is notifiable works.
So you will need a registered electrician to provide an RCD-protected fused connection unit outside the bathroom itself.
I would also ask him to fit a timer as you do not need/want the radiator on 24 hours a day.