Flack was educated at Leeds University and the College of the Resurrection at Mirfield, he was ordained in 1967.
He is a former Bishop of Huntingdon. After curacies at Armley and Northampton he was Vicar of Street James Chapelthorpe from 1972 to 1981. From here he rose steadily in the church"s hierarchy, being successively Team Rector of Brighouse, Rural Dean of Elland and Archdeacon of Pontefract before his ordination to the episcopate.
He was subsequently Director of the Anglican Centre in Rome until retirement in 2008.
Flack is now an honorary assistant bishop in the Diocese of Peterborough. and the Diocese of Ely.