Thank you 1949, your time and effort is appreciated. It sounds like my chances are slim to non - existent of finding this one.
However you never know one day I may get lucky, probably the same day I find a 1933 in the same envelope or on eBay as a two for one deal.
I am going to keep looking but in the meantime the next time I am near the British Museum I will pop in and hopefully see it for real.