The GB saddles look like they can take any rail mounted bag, but they also have some features on the saddle hardware which look like they are there to attach things. I worked out these are for something called a KlikFix saddlebag connector. But the saddle bags I've found that use Klikfix seem to be a lot larger than I need for tube-tyre levers-tool.
Does someone make smaller saddle bags that use Klikfix or will fit on the older "leather loop" style. Something in the 0.5l to 1.5l would be about right. The Brooks Challenge is a bit fiddly for my taste.