Keys were lost to this old (pre 1984) style garage door lock in the Forest of Dean. A key could be obtained to the code on the lock but that leaves the missing key unaccounted for. Simplest and most secure was to pick the lock on the back of the handle to enable it to be replaced for a brand new lock.
Although the lock above is Union branded they are commonly seen with the L&F variant instead. There are dozens of different designs of garage door locks.