Hill For Leathers. In a village called Ash, Near Aldershot. I’ve used them a few times and so does Motolegends . They specialise in bike gear of all types.
Spence professional leather repairs, wolverhampton . James did a dianese jacket for me that wasnt new but was too good to chuck. he does textiles, leathers, boots top quality jobs 01902 780902
Another possible to add to the list is Richard Kemp aka “The Tilehurst Cobbler” near Reading.
I don’t know if he repairs biking garments but he did an amazing repair job on the zip in my biking ankle boots by return of post, I’d happily use him again for any repairs I might need.
I had a zip replaced in my Rukka jacket at Hideout Leathers near Saffron Waldon. booked in advance and the job was done while I had a coffee down the road. It took about 2 hours, they replaced all the tapes and fitted a YKK zip.
It cost about £130 that was £100 cheaper than another repairer mentioned in this thread.
I can’t recommend them highly enough. Lovely friendly and helpful people. You can also post the jacket to them.