Thought I had a solution .... local carpet shop have a machine than whips the edges of off-cuts to turn then into rugs, spoke to 2 of the staff there ... they said 'no problem'
But when I called back (several times) to get price, they seemed very reticent, now they advise don't think it will do an internal loop. So back to looking for a solution.
If I could find an upholsterer maybe sowing on an edging tape (like wrapping cut edge in a U shaped piece of fabric) ... maybe a way forward.