After further scratching around on google i've decided that no one knows. Harold might have been a great orchid grower but it seems he didn't keep good records.

So what is the worry?

Is it a species orchid or a Hybrid?

Does it go in Class 24. Non Vandaceous Species from Other Areas

Or

Class 26. Other Genera Hybrids

Doesn't matter all that much seeing I'm only ever likely to see the one plant in my lifetime. I'll have to make a decision next time it turns up at a monthly society meeting.