Footsore's Inter-War period covers the period between the two World Wars (1918 -1939), but its main focus is the imaginary Very British Civil War (VBCW), set in 1938. The background to this fun and interesting "what if" period can be found in the many books published by Solway Crafts, but basically is as follow.
King George V dies in 1936 and is succeeded by his son Edward VIII. Edward abdicated soon afterwards so he could marry his lover Wallace Simpson. That's the real version. In the "what if" scenario he refuses to abdicate and marries her causing a constitutional crisis. The government resigns and Parliament is dissolved. Oswald Mosley of the British Union of Fascists is invited to become Prime Minister. The outcry over such a move causes an outbreak of conflict between a multitude of different factions fighting not just the fascists but for their own causes too. If you want to inject some imagination into your historical wargaming there no better place to start.