I've looked at this before as well. There isn't a designated landing gear lever or flap lever, is there? Being such an early design, my past thoughts have been that this lever was connected to the hydraulic system, and the pilot had to pump the lever to work the various mechanics that worked off the hydraulic system. I say this, because right next to that pump lever are four separate valves/clutches, one for the landing gear, one for the wing flaps, one for the wing fold, and another I've never been able to make out (though I assume is for the bomb bay doors). Each has neutral positions as well as extend/retract positions. My thought has been that, in order to raise/lower the gear, the pilot had to use the landing gear valve/clutch, put it in the proper selection, and then pump until they were extended or retracted, and the same would go for all of the other hydraulic functions. I have heard it referred to as simply the wing fold hydraulic pump lever, but I think it had to be used for all of the hydraulically controlled functions, not just the wing fold alone, based on the fact that there are valves for each, right next to that lever.
The aircraft is such an early design, it was the first to have hydraulically assisted wing folding, and it came about while retractable landing gear (and flaps) were still much a new thing.