Today is the anniversary of the 1944 by-election in West Derbyshire. It took place under the terms of the wartime electoral truce, which meant that the candidate of the incumbent party should not have faced a challenge from the other major parties.
The Conservatives held West Derbyshire before the by-election. They lost the seat at the by-election to an independent Labour candidate.
The Conservative Party interpreted the wartime truce as a political cease-fire, suspending almost all party activity and abandoning its annual conferences. While the Labour Party stuck to the letter of the electoral truce, it maintained a more active political machine and reaped the benefits in the 1945 election.
At West Derbyshire the rules of the truce were stretched. The winning independent Labour candidate had previously been a Labour Party candidate and re-joined the Labour Party after winning the seat, but for the duration of the by-election campaign he was independent. The Conservatives, with some justification considered that the seat had been stolen from them. The Labour Party could, however, claim that they had stuck to the letter of the truce.
The lesson here is that two parties can enter into an agreement in good faith, but interpret that agreement differently. Tony Blair and Gordon Brown would probably agree.