What size needle does a John Lewis mini seeing machine need?

Question edited for clarity.

The problem is that John Lewis didn't make it, they just got an established maker to put the John Lewis name on it.

Is this it?
https://johnlewis.scene7.com/is/content/JohnLewis/237219925mnl1pdf?

Apparently made by Janome, the Janome 5050

https://groups.google.com/g/uk.d-i-y/c/uy4L3GM6_VM?pli=1

This one?

https://www.johnlewis.com/janome-5050-sewing-machine-white/p2253577

https://vickikatemakes.wordpress.com/tag/jl250/

A lady here has the manual

https://www.homeownershub.com/uk-diy/john-lewis-jl250-instruction-book-3067198-.htm

..

John on my antique treadle machine if I put the needle in wrong it jams , don't know it that's your problem or not. I would also try new needle this one could be bent gl

Try contacting these folks. They will tell you what is available for your machine:

Sewing Machine Parts Accessories Sewing Supplies John Lewis

Is this what you are looking for?

https://drive.google.com/file/d/0B3crT89BHvGiOTc4SnJBVmhOR1E/view

try changing the needle
also the machine could need some type of adjustment, only a sewing machine repair technican can say for sure

the best advice is having the machine serviced, but here are some other suggestions

This was really helpful for me fixing my daughter a John Lewis (janome) mini sewing machine, and now can get the bobbin thread up again, however, when you sew, the thread is not staying in stitches, just coming off the material completely. I tried forcing the gears on one more time but then it didn't pick up the bobbin thread again so went back to the other gear position. Any ideas of what to try and get it stitching again? Thanks

The motor is tired or dry and perhaps the belt is slipping.

is the needle inserted correctly?
is it the right needle for the fabric being sewed?
it's possible that it could also be a timing problem, which means it would have to be check at a sewing machine shop

have you tried changing the needle?