Last time this happened to me on my Roberts. Campag BB cup was stuck on drive side. Best way I found was to clamp the two large flats of the cup into a vice mounted to a workshop table, this way you have the hole frame for leverage. When this happened to me with cups that did not have flats, or on the non drive side, I used a file to make 2 flats on the cup (it is still useable after, just less pretty) so I could put it in the vice. This was always successful, but maybe this was only luck...
I had this problem on several frames.
Last time this happened to me on my Roberts. Campag BB cup was stuck on drive side. Best way I found was to clamp the two large flats of the cup into a vice mounted to a workshop table, this way you have the hole frame for leverage. When this happened to me with cups that did not have flats, or on the non drive side, I used a file to make 2 flats on the cup (it is still useable after, just less pretty) so I could put it in the vice. This was always successful, but maybe this was only luck...
Hope all goes well for you!
L