I doubt I would have seen a Derber shoe shop where you saw one. I tended to shop East of Regent Street. There were a number of Sacha shops around there, and I had 'previous' at a man's shoe shop called "Topper" that may have been around Carnaby Street. Shelly's were also around there.
We are talking a good number of years ago, and things that may now seem important were fairly trivial to me back then. I was always into girls who wore heels (I have a theory that heel height is directly related to libido - though not exclusively so) and shoe shops with stiletto heels weren't that unusual. There were very many more shoe shops back then: FHW, Dolcis, Saxone, Faith, Sacha, Ravel; some of which made it to >> this list << some didn't. Derber is not listed. I say "I was into girls who wore a heel", is half the story. I might be into them initially because they could and did wear a heel. I had many girlfriends who were eager to please, so chose clothing/footwear they knew would appeal to me. That situation still exists to a degree even now, but less so. Getting older, losing the shape that made any clothing look attractive, is another reason youth is often wasted on the young.
It wasn't at all unusual back then for single shop, or a small group of shops to be run by a 'sole trader' entrepreneur, and London's West End provided enough business to keep even the wildest retailer in business - at that time. Rents and rates prevent this now, and may well be the reason why bigger groups seem to thrive - though you don't get much bigger than BHS.
Had I the benefit then of second-sight, I would have made it my life's work to document what has always been a personal interest in social anthropology: The British shoe manufacturing and retail industry. All that diversity, an industry known world-wide, all just about gone thanks to cheap imported (and largely rubbish) footwear.
I think if this line of thought/discussion is to continue, it ought to have it's own thread.
Hopefully in a day or two (when yet another 'rush job' is put to bed), I'll be able to do a full write up of Sundays adventure.