There are two books on English silver hallmarks available on Amazon, the other being English Silver Hallmarks, and although both are excellent books, in my opinion, this is the lesser of the two. Both books are almost identical in content: both provide illustrations of English, Irish and Scottish silver, gold and platinum hallmarks, and illustrations of the more important makers marks, which allow for the dating of silver, gold and platinum items. However, this book omits Sheffield plate marks, which are included in "English Silver Hallmarks", and it is harder to find what you are looking for in this book.
The periods of time covered by these two books are slightly different. This book gives hallmarks for the period from 1300 to 1991, whereas "English Silver Hallmarks" covers the period from 1554 to 2004. If you are wishing to date very early pieces of silver, then, clearly, this is the book to buy. However, as I have never had any need to date items made prior to 1554, and most of the items that I have dated have been more recent items, I find the period of time covered by "English Silver Hallmarks" to be the most appropriate for my needs.
Although both books are very useful and both are likely to satisfy the requirements of the average silver collector, if you are only going to buy one of these books, then "English Silver Hallmarks" is probably the book to buy.