Fr Derek Allen was born on All Soul's Day 1925 in South Croydon and educated at Eastbourne College until he was evacuated to Radley soon after the outbreak of war. In 1943 he worked briefly for the Foreign Office before being called up  in 1944, serving in the Royal Signals Corps. It was in the Army that he found his vocation.

In 1947 he went to Oriel College Oxford where he distinguished himself academically, gaining a First Class degree in Theology, before going to St Stephen's House where he was to spend much of his life.

He was made deacon in 1952, serving his title at Christ the Saviour, Ealing until he went back to St Stephen's House as Chaplain. For two years he was appointed Lecturer in Theology at Kings College London and Sub-Warden of the Hostel before going back to "Staggers" as Principal in 1962. There was a two year gap between his departure from Oxford and his appointment to St Saviour's - this was spent at the Convent of St Mary, Wantage.