Wegg-Prosser attended Downside School, then studied at Oriel College, Oxford and became a solicitor.
In 1934, he joined the British Union of Fascists (BUF), soon becoming director of the group's Shoreditch branch.
[1][2] Wegg-Prosser became disillusioned with fascism, making contact with anti-fascist activists, and leaving the BUF at the end of 1937.
He then began speaking out against the group's anti-semitism and fondness of dictatorship, and was admitted to the Labour Party, on a year's probation.
[1][2][3] His grandson Benjamin Wegg-Prosser was Tony Blair's Director of Strategic Communications at 10 Downing Street.