You can buy a kit to re-enamel it. I did it on our old bath. It worked and the result was brilliant. I did notice after a few months or so, it started to have tiny little bubbles but you could only see them when in the bath. (So a buyer wouldn't notice them on a viewing!)
It smells really strong when you apply it and the bath has to be cleaned really well and sanded before applying the enamel. Its very hard work but well worth it. I think B&Q sell the kit, DH got our one from Robert Dyas.