Only Greens Senator Peter Whish-Wilson (right) was game enough to raise the issue of political donations by the big four.

In last week's corporate tax transparency data from the Australian Tax Office, you won't find any data on four of the country's biggest political donors and most influential policy advisers.

In recent years, the big four consulting firms -- PWC, KPMG, EY and Deloitte -- have quietly secured a key position in the soft corruption of Australia's federal political system, exploiting the Coalition's agenda of outsourcing of policy advice to secure billions of dollars in consultancy work while buying access and influence with millions in political donations and the hiring of former politicians and staffers.