Why did the Royal Doulton Lambeth factory close, and what changed after 1955?

Royal Doulton states that new city regulations prohibited salt-glaze production in 1955, forcing closure of the Lambeth factory and moving production to Stoke-on-Trent. For collectors, this helps with dating: a true Lambeth-made salt-glaze era piece belongs to an earlier chapter, and post-1955 output ties more strongly to “The Potteries” in Staffordshire. Britannica’s summary of Doulton ware also places the end of the Lambeth factory in the mid-1950s. If you collect Lambeth items, this closure is a major historical marker, separating London stoneware tradition from later Staffordshire-led tableware and collectables.