Although I am sure there are other books out there covering Britain specifically, I recently read Horne's To Lose A Battle which addresses this question mostly in relation to France. But many of the points in its first few chapters apply to Britain as much as to France.

As well as the obvious reluctance or ability to spend big on materiel, rapid technological advances (in aircraft and armoured vehicles especially) meant the defence chiefs were reluctant to order large quantities of hardware. This led to some units being very poorly equipped when war did break out, even if their weapons were only a few years old (many of the light-bomber units of the RAF for example)

The carnage of 1914-18 also meant the British were determined to avoid war at almost any cost. Although networks of alliances with the smaller Eastern European nations (Czechoslovakia, Poland, Hungary, Yugoslavia) was led by France, the British also took the position that Germans could be discouraged from expansion by being surrounded. The willingness though of the western allies to sell out their allies to appease Hitler though showed up the weakness of this strategy though.