Anyone want to quickly settle a Friday afternoon debate in our office?

What's the difference between an O&M Manual and the CDM H&S File?

I'm convinced I'm correct with CDM H&S files being retained by the building owner/operator following a notifiable project - construction and subsequent operation of a building. O&M Manual provided for work undertaken that might not be notifiable or falling outside of CDM.

Willing to be corrected by the learned colleagues on this forum however!

The difference, in short, is they are two distinct things (although the master records for both can be kept together).
I've never been entirely content with the H&S File being so distinctly linked with Notifiable Projects (and I've yet to see a good H&S File). The best-practice Facility Manager will make-up and maintain a H&S File irrespective of any Notififable works. There are a great many lesser projects (not meeting notification thresholds) which can significantly impact on future works, maintenance, cleaning, etc.
Sadly, I still see "H&S Files" being made up for Projects, as opposed to being maintained and updated for the relevant structure.
The Construction Industry and Clients generally are IMHO still a long way off from CDM compliance in this respect. Some of the web-based systems now available give hope for the future.