Sadly, I suppose the decline in home dressmaking has dealt the death blow to many small fabric shops. There is a revival in knitting and "specialist" wool shops though where you can get advice, exotic wools, patterns, instruction - and in my case an emergency repair on a very complicated and expensive long waistcoat I had just finished and worn in to show. If anybody is in my area, The Wool Shop in Olney with wonderful Ana (Spanish) dispensing advice and enthusiasm in equal measure! I know this is advertising, but worth it. As the French say "Vaut le voyage"!!
I used to buy all my fabrics and patterns from a little shop near Richmond station (about 40 years ago!) and also Laura Ashley where I bought remnants of both dressmaking and furnishing fabrics which were made up into little pinafores and dungarees for the DDs.
John Lewis has reduced its dressmaking fabric section to a fraction of what there used to be but on the plus side it is now on the top floor, tucked away from all the hustle and bustle and best of all next to the coffee shop!