It's a 'Nash' shell as said above. I have a complete set of lugs, BB shell etc. along with loads of others in the stuff my late friend had. Can still be found on the Ceeway Marketing website.
I dug out the complete set of 'Nash' lugs that I had and took a piccie. They're a bit 'tarnished' but you can see the 'flats' on the lugs and seat cluster.
Quite a hefty BB shell I reckon.
Apart from Tel's frame I've not seen any built into a frame as far as I can recall.