The Handbook of British Mammals
Corbet and Southern
This volume is probably more a historical document today but use it alongside any modern Field Guide and it works wonderfully. Just don’t go looking for Coypu in East Anglia today, they were probably eradicated by the early 1990s.

Part of the seven and a half pages that covers the Harvest Mouse in Great Britain in The Handbook of British Mammals

As usual, Collins publish excellent Field Guides to Mammals. Such a volume works brilliantly alongside a good reference work such that by Corbet and Southern
I suppose at some point I ought to purchase the most up to date version of a handbook to British Mammals, however much of the salient historical and biological data in my volume is still correct and I supplement this with species specific detail in other volumes on my bookshelves. Perhaps the most relevant aspect is that not only am I a naturalist, but I am a reader of books too. Corbet and Southern’s volume has prose as well as fact.
Good information is included on the Classification of Mammals and I am especially pleased that detail on extinct species is included, such as Brown Bear and Wolf. Hopefully in my time the latter species may be reintroduced to Scotland.
Line drawings of dentition and skulls are included and the systematic accounts, each written by an authority, are broken down in to Description, Measurements, Distribution, Habitat, Behaviour, Food, Breeding, Predators and Mortality, and Relations with Man.

A very good, reasonably priced series of books was published by Whittet Books. Updated and new editions are available. Written by acknowledged experts in their field, these are very accessible and in no way daunting, but still give good information on species. Some authors of these volumes also wrote the species accounts in The Handbook of British Mammals
Book from my shelves:
The Handbook of British Mammals, G B Corbet and H N Southern. Blackwell Scientific Publications, second edition 1977. ISBN 0 632 09080 4