Despite thinking it was a long shot, thanks to @PWA 1967 I was able to source a high grade 2+A 1953 farthing a lot sooner than I was expecting - I'll share some images over in the coin acquisition of the week thread when it arrives.
So here's an even greater long shot...
Last March this CGS 85 ex J.B. de Loynes 1953 VIP proof farthing sold through Noonans for £280:
This sale came before it was known that some VIP sets contain a previously undiscovered 1953 variant (discussed in this thread) where the 'F' in 'FARTHING' points to a gap and the 'I' points to a bead. From doing a small amount of research it seems like a 50:50 split whether a VIP set contained this variant or the more documented 1 + A variant.
I'd like to offer £560 for this coin pictured (double the hammer price), something around that amount for a similar grade, or £250 for a lower grade example which is clearly this variant.