The big four banks are expected to contribute equally to a social impact investment fund established by the federal government, but hint they would prefer to supply debt to the fund than invest in it directly.

ANZ Banking Group, Commonwealth Bank of Australia, National Australia Bank and Westpac Banking Corp are understood to be considering each stumping up $50 million to fund small companies that deliver social impact, as well as investment returns. Their contributions would be matched by the government, taking the total fund to $400 million.