John McDonnell has warned bankers they face public "opprobrium" if they return to spiralling wages and bonuses as he claimed a repeat of the 2008 financial crash could be imminent.
The Shadow Chancellor said that not enough had changed in the City since the economic crisis and suggested the same institutions were "set to fail again".
In a wide-ranging speech on the economy, Mr McDonnell set out Labour plans for a "kitemark" scheme for good businesses which offer the living wage and pay taxes "fairly and transparently".
Speaking in the City of London, Mr McDonnell called for reform of the banking sector, breaking up the "failing monopolies" and creating a system of German-style regional and local banks.
Since 2008, he said, "nothing substantive has changed - the same failed institutions we had before the crash I believe are all set to fail again."
The concentration of banking in a small number of high street lenders was part of the problem, starving small businesses of credit, he added.