Abstract
This article analyses the role of intelligence in the relationship between Britain and France before the Second World War based on a thorough examination of both the British and French diplomatic and military archives. The German challenge forced decision-makers in London and Paris to consider closer strategic cooperation to counteract the Nazi threat. British and French officials understood that in the end if war with Germany came, both countries would need to allies to win. However, before 1939, efforts to cooperate in intelligence were frustrated by Britain's reluctance to form an anti-German alliance with the French. Political considerations limited intelligence sharing, and knowledge about each potential ally's intentions and capabilities were shaped by political and cultural misunderstandings. Extensive and systematic pooling of information between London and Paris was therefore not formalised until planning for war began in earnest in April 1939.