@oldbuffer - thank you so much for your reply. The plug is out!
I really appreciate your help. I was minutes away from trying to undo the grill part, so I think you may have saved my bath.
Thanks again.
The plug for the waste outlet for my bath recently stopped working and to fix it I would need to open the side of my (very much tiled in) bath. As an interim solution, I just want to remove the plug and use a cheap "traditional" plug instead, but I cannot for the life of me get the plug out. The...