It’s curious - somebody has gone to the trouble of making up a double-ended key which cannot be attached to a keyring etc. Looks like the left bit has been brazed on. Probably late Victorian/Edwardian?
Usually these are burglars’ skeleton keys, but these are real ones. The right bit is overlapping hook wards - a pattern which practically cannot be skeletoned but which makes the key weak, so is only used on either very small keys, or very large ones. Most likely reason is the convenience of only 1 key, in effect, to carry. Or maybe easier to hide … ?
