The Square Peg

The Square Peg is a 1959 British comedy film starring Norman Wisdom and directed by John Paddy Carstairs. Norman Wisdom plays two different characters a man who digs and repairs roads, and a Nazi General.

The two are posted to France, but mistakenly end up behind German lines. Grimsdale is captured by German soldiers and taken to local headquarters in a chateau. Meanwhile, Pitkin has wandered into the nearby town, but doesnt notice soldiers standing to attention and saluting him. It transpires that hes a double of the local commander, General Schreiber. In a cafe, he recognises the waitress as Lesley, an ATS officer he had briefly met in training camp. She is in fact an undercover agent working with the local resistance group, but Pitkin inadvertently blows her cover and shes arrested, along with the cafe owner.Pitkin and Henri, another resistance worker, break into the chateau, using a tunnel that Pitkin digs, but they too are captured. Pitkin comes facetoface with Schreiber and finally realises his chance. To keep up the deception, he has a tryst with Gretchen, the generals mistress a singer of Wagnerian proportions and comically attempts to sing Schubert lieder with her. ........

Source: Wikipedia