Although ‘Windsor’ is a place to the West of London, your cup and saucer was made in Longton, Stoke-on-Trent at the ‘Windsor Pottery’. The Pottery was originally operated by Hill & Company but transitioned to the Co-operative Wholesale Society Ltd (CWS) during the period between 1911-1920.
They used a variety of marks, but that particular mark dates from about 1950 onwards. The business was sold to Hammersley and Co (Longton) Ltd. in 1971, who then ran it under the name of ‘Royal Windsor’.