Stewart's father served with the King's Own Yorkshire Light Infantry and was regimental sergeant major of the 2nd Battalion, Parachute Regiment during the Second World War, having previously worked as a general labourer and as a postman.
Ayah Stewart bertugas dengan King's Own Yorkshire Light Infantry dan merupakan sersan besar resimen dari Batalion 2, Resimen Parasut selama Perang Dunia II, setelah sebelumnya bekerja sebagai buruh umum dan sebagai tukang pos.