Hello Mrs. Nowell, typically copies of Encyclopaedia of British Pottery and Porcelain Marks as published by Herbert Jenkins in 1964 sell in antique shops at the 15 to 25 GBP level and with an inscription, the additional value is modest as the author is not a "celebrity" or a figure well-known outside of the industry. At auction and in online sites, this book can sell for 5 to 10 GBP. To a collector with a signature and inscription, perhaps it would be worth 25 GBP.
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