Thanks TheAFSB for the rubber recommendations. There are the shops to go to.
More generic kind of sex shops for fetish wear:
Harmony and Ann Summers (several central London locations)
More authentic creative fetish stores and my favourites:
FAB/ Fetish Alternative Boutique in Camden market (latex, harnesses, accessories, toys)
https://fab.london
No Wear, also in Camden market (handmade unique Burner style fashion)
http://noweardesigns.com
Sai Sai/ opposite Camden market (Gothic style black alternative fashion like corsets, capes etc)
Camden market has a variety of stalls and vintage stalls and boutiques where one can find alternative clothing, however it got commercial in the last few years...
For more edgy designers and rare finds there are markets which take place regularly in a bar with drinks and socialising:
LAM/ London Alternative Market
https://londonalternativemarket.com
LBB/ Le Boutique Bazaar
https://www.leboutiquebazaar.net (Visit their Insta for tickets and more info, next one is on 02/04)
Charmskool Pop up events
https://www.eventbrite.co.uk/e/charmskool-erotic-pop-up-shop-social-tickets-560465115247
Let me know if you have more questions there, I am happy to help as fetish fashion is my speciality