Harry Hall?? never heard of the brand/builder over here in the US, but it seem like there so many brands out there that have names that remind me of my highschool teachers, for some reason.....
About the shift levers, From what I see in the pic, I think those are late model Simplex retrofrictions adapted on to an earlier Simplex downtube clamp (Clamps originally came with the earlier solid version of the levers,without the cutout. Simplex supplied Mavic with similar retros but sans clamping band and Simplex brand stamping, so there is a sort of relation to Mavic with those shifters.

Chombi