There is nothing in UK law which says that suppliers or manufacturers have to give a one year warranty.
Unfortunately for retailers, including resellers such as plumbers, there is actually no law that forces a manufacturer to offer ANY warranty. The onus, ultimately, is on the retailer to observe the requirements of the consumer protection legislation
There is... contract law!! Any reasonable sized company will/should have a buying contract with their supplier(s). Part of that buying contract will be what happens (commercially speaking) with 'faulty' products.
Alternatively, a retailer can opt to purchase products
without warranty (again stipulated in their contract(s)) at a discounted price.