The Portuguese Expeditionary Corps [C.E.P.] was the centrepiece of Portugal’s intervention in the First World War. It was despatched to France in order to secure international plaudits for Portugal and its young republican regime, in place since October 1910. This political objective required the C.E.P. to be as independent a force as possible. Unfortunately, the C.E.P. failed to impress its senior partner, the British Army, whose High Command soon lost faith in it, applying pressure to the British Government either to remove the C.E.P. altogether or to limit, as far as possible, the Portuguese presence in the trenches. Despite this, in November of 1917 a ‘Portuguese Sector’ was constituted in Flanders, with the two Portuguese divisions fighting side by side. This article investigates the nature of the misgivings between the two armies and considers why, in such a charged atmosphere, the British High Command was forced to give way.