The two easiest ways to break the lock are vicegrips or the screwdriver.
If the lock is not recessed large vicegrips with GOOD teeth can usually be locked on, (MUST use the side of the jaws). The lock can be turned, though this will damage the wood just enough that the lock can be turned. The lock can then be turned back to lock again, though a key will never be needed.
If the lock is recessed, (due to vicegrips, making the "spin ring" useless) the large screw driver is very effective. However. many people can't turn it. "pliers" are worthless. Use a large adjustable wrench closed on the flat edge of the screwdriver, next to the lock. If there is not enough room on the flat tip of the screwdriver for the adjustable wrench, the the screwdriver is not big enough anyway.
At last resort, try putting a BOLT onto the key hole. It must have threads for wood, so it has a point, obviously not a bolt made for a nut. And it must be a bolt, not a screw, so you can use a wratchet or a wrench. It will not work using a screwdriver.
All these are much simpler then they sound. And they all take less then a minute if you are doing them correctly.
Good luck.
Steve