Hi Bernard,
Stonier appear, according to Companies House, to have become plain Stonier and Co Ltd, in 1911, and appear to have existed, in one form or another until 1997, when the company underwent a name change to Stuart Crystal Marketing Ltd, now a dormant company. However, the registered office is given as Barlaston nr Stoke on Trent, Staffs, so possibly more info on Stoniers may be to be found at Wedgwoods?
Regards,
Marcus