Dave,
I'm thinking that your London LP should be a microgroove pressing. I suppose technically you're correct, that the shape of the groove is a V looking shape however that groove opening is wider than the later stereo cut grooves. In fact, the grooves on LP's started out wider and progressively got more narrow over time. When Columbia introduced their microgroove pressings, manufacturers complained about how narrow the grooves were in comparison to the earlier records (i.e. 78's)
As Lewm mentioned, the U shape description is just a vernacular term for specifying the difference in dimensions in order to clarify the point being made. Mono cartridge makers will use a nude conical stylus because of those earlier groove dimensions.
I'm thinking that your London LP should be a microgroove pressing. I suppose technically you're correct, that the shape of the groove is a V looking shape however that groove opening is wider than the later stereo cut grooves. In fact, the grooves on LP's started out wider and progressively got more narrow over time. When Columbia introduced their microgroove pressings, manufacturers complained about how narrow the grooves were in comparison to the earlier records (i.e. 78's)
As Lewm mentioned, the U shape description is just a vernacular term for specifying the difference in dimensions in order to clarify the point being made. Mono cartridge makers will use a nude conical stylus because of those earlier groove dimensions.