Replacing A Cold Water Tank in the Loft

A relative was having issues with their cold water overflow constantly dripping water. So I went into the loft to check out the float valve with the idea that changing this would solve the problem. Unfortunately things were worse than I could imagine, the float valve was indeed faulty, however what was worse was the cold water tank which was disintegrating as I touched it. The only sensible option was a replacement tank, so here's the video.

[@stuartmainwaring9570]

I have one of these but also a combo boiler. Do I need this tank still?