Trade Plumbing supplies shop (Plumbers Merchant) like this example in Nottingham https://www.openstreetmap.org/way/284792269 shop=plumbing_supplies 

There are also https://www.willbond.co.uk/ bathroom showrooms https://www.openstreetmap.org/way/61568326 shop=bathroom_furnishing perhaps

The Ilkeston Plumbing Centre looks like a Plumbers Merchant or plumbing supplies shop