Does anyone know how to remove the gas cap on the M3W?

It has six bolts, one of which is under the hinge and another under the lever. I can't fathom how on earth to get those things out without breaking the pin that holds them on. I ordered some ultra low profile hex wrenches but don't have a lot of faith that they'll clear it.

While I've not had my gas cap assembly off my M3W yet, I have two other cars with similar design 'Monza' style caps, and the top hinged portion of the cap is threaded onto the adaptor/base (the bit with the six screws). Normal RH thread, btw.

Good quiestion. I tried to remove mine last year but ran in to the same problems. At the time I was trying to remove the lockable gas cap, which had been stuck. Luckily we finally got the locking cap out, so I gave up on removing the gas cap. I've since taken othes' advice and nver put the locking cap back in. But I'd like to hear how this is done anyways.

This image might help.

There's one for sale on Ebay https://www.ebay.co.uk/itm/403695986129 with several pics from different angles

That's looks like the Newton Equipment 'Classic' range

Newton Equipment

The seller lists it as "monza style fuel filler cap / morgan 3 wheeler", he's located in Malvern which somehow I find a bit worrying.....

It certainly does look like a Newton unit. I reached out to them about disassembly.

I'm guessing the whole cap is threaded on but if it is, my god is it on tight. I'm probably going to try taking a spanner wrench to it to see if I can get any movement. I've looked for any sort of locking ring or pin without luck so far.

That is good information, thank you.

They may have stuck some form of loctite on the threads. Perhaps a bit of heat ( heat blower rather than naked flame!) may help loosen it.