ER.103 was drawn up to provide a research aircraft to investigate the transonic and supersonic flight regime. The Royal Aircaft Establishment firmly believed that a delta wing possessed the correct characteristics for this regime, a belief that probably led to the cancellation of the Miles M.52.
Fairey had already produced the FD.1 point defence interceptor demonstrator, so had experience of delta wings. The Delta 2 (or as Fairey referred to it in their paperwork as the "Type V") would be powered by a single Rolls-Royce
Avon engine.The FD.2 was a world-beater, taking the Absolute World Air Speed record in 1956. On the basis of this various variants were proposed, including one with underwing Napier ramjets. Fairey further developed the delta concept with the Delta 3, a heavy fighter to meet
OR.329.Interestingly, Marcel Dassault has been credited/charged with/blamed for taking the basic FD.2 and turning it into a fighter - the Mirage III. Another world-beater.
Later, in the 1960s, as BAC was developing Concorde, one of the FD.2 aircraft was converted to an ogee delta wing under
ER.193D. This provided valuable data for the Concorde programme.