However, this is actually a poster with a story! Cathy, who's Nekoglyph on flickr, kindly left a comment to explain. Her photograph of the poster got a response from the owner of the shop. It turns out that the advert hasn't been hanging around for decades at all, but was pasted up for filming of The Royal - a period hospital drama filmed around Whitby and Scarborough.
While the Scarborough poster may be a cheeky impostor, the History of Advertising Trust has a lovely image of the original. (And when you visit their site, don't forget to have a look at the Ghostsigns archive!)