Help Identifying Year & Maker of Vintage Watch Please

Hi all, I'm new to the forum. I'm a watch enthusiast and modest collector. I wonder if anyone could help me identify the date and movement of a gold tank watch I've owned for a couple of decades.

The hallmark seems to read London (import omega sign) but the year, M in an oval, oddly looks much more like a Birmingham stamp of 1886 than London of 1907 or 1927.

The Sponser's mark would appear to be George Stockwell and in the centre of the back of the case there is a mark or emblem that I cannot make out, it looks like an aeroplane.

I have seen the GS sponsor stamp on Movado / Asprey, CYMA / Tavannes, Jaeger LeCoultre and Ernest Borel & Cie, and the only movement I've found to look the same is made by Borel & Fils.

My watch movement measures approximately 23mm across x 2.5mm thick

I've uploaded a number of photos of my watch and a couple of photos of the Borel movements to this google photos link https://photos.app.goo.gl/FMhS9WvVGclL9BgI2 . Any help and info would be greatly appreciated.

Thanks, Dave.

London 1927
you can find info about Stockwell and watches of the era here...http://www.vintagewatchstraps.com/sponsorsmarks.php#g

I would need to see the setting work under the dial to try and identify the movement