It may well be plastic coated. From what I remember from DT at school the metal is heated up and then dipped into a big pot of plastic powder, which melts onto the surface. Therefore heating it up and scraping it off is the only way to get it off really.
I think you have hit the nail on the head there Adam.
This stuff is really thick (like 2-3mm in places!) and certainly behaves more like plastic than powder coat. I don't know why I didn't think of that before?? I used to teach hot dipped plastic coating when I was at school.
Where water hasn't got in under the surface, this stuff is bonded on SO strong! Heating & scraping doesn't seem viable because of the mess it makes...I guess I'll have to try the bonfire trick or see if there is anyone local that can remove this stuff.
Thanks for the offers of sandblasting....Joe, Alan etc...might be giving you all a call sometime very soon
Thank you everyone....I'll let you know how I get on with my quest to remove this stuff.