The section headed 'Warning Unit' in the AAIB report on the (unrelated) G-IWRC crash back in 2007 makes interesting reading:
The Warning Unit is mounted near the top of the
instrument panel and generates the visual and audio
warnings for a number of systems. A memory within the
unit stores, in chronological order, the last 31 warnings
generated when the helicopter is in the flight condition.
Whilst there is no timebase to determine when each
warning was generated, there is a flag within each
message code which toggles at the end of each flight.
Consequently it is possible to determine the warnings
which were generated during the last flight.
Edited to add: DAPT, you beat me to it by seconds!