Bought it from Homebase its called Hagesan Blue. It's a professional limescale remover, I've used it all over our bathroom tiles, the taps, shower and everything is shiny and lovely.
Thought I'd give it a try on the steel sink and taps in the kitchen and OMG I HAVE A SHINY SINK!!!!! .
My DH thinks it's very sad to be so excited about cleaning but it's such a good product I had to share it!