Category 5 regs 3.07.4 states
(a) A companionway hatch shall be fitted with a strong securing arrangement (e.g. latch), capable of securing the hatch in a closed position, which shall:
(i) Be operable from above and below including when the boat is inverted.

I have just fitted a new hatch which works slightly differently to the last one and am pondering how to comply.
My thought was to use a spring loaded bolt that has a slide 'handle' on both sides, but I don't seem to be able to locate such a thing .

How does everyone else comply with this?

we use a piece of 4 mm rope with a cleat either side very quick to install and fail safe to use

Yep, like Boty mentioned, I used to have a 4mm rope tied to the hatch that went to a jam cleat. I like the idea of a cleat either side, as the rope used to get in the way a bit.
The current boat has two latches that dog the hatch closed with handles either side. This is what I wanted to do on the last boat, but I couldn't work out how to engineer it, and the rope idea worked fine.

Previous hatch had a handle & door knob setup that was a bit clunky looking and had a tendency to be very stiff.

The rope method looks like the way to go.

Thanks!

From what I've observed it's quite common during an equipment audit to grab a crew member or the owner, lock them down stairs, and ask them to get out. Make sure you know how to use whatever system is chosen