A beautiful Singer 15. I believe those are RAF decals. I may be wrong.
Manual is here:
https://www.singer.com/en-ca/search/support?title=15
Download the first one on the list.
All the parts you might need are easily available. Singer's most popular model. Made for over 100 years. Singer still makes them in India. Go to the Singer India site and you'll see them both motorized and in treadles.
This machine was copied by lots of manufacturers both in Europe and in Asia. Lots and lots of clones out there. You have a beautiful original.