This problem is over.
Yet another padlock has been fitted that seems to work well with the keys already in circulation and some brand new ones. So if you've got an old key that is obviously worn thin, bent, fractured or dubious in some other way, then please post it back to Malcolm Reid (the MLCMAC Permit Sec) to get it replaced on a free issue basis. Otherwise your usual key should be OK.
Stuart France
Conservation/Access Officer
Cambrian Caving Council