The banking royal commission turned its attention to the superannuation industry this week.

Why? Because the super industry has endured years of scandals, and who should administer the massive pool of retirement savings is hotly contested in Australian politics.

How large is the pool of savings?

Australians hold $2.6 trillion of assets in their super – equivalent to 144% of our nominal gross domestic product – and the value is growing relentlessly because workers are forced to dedicate at least 9.5% of their wages to super every year.

Michael Hodge, senior counsel assisting the royal commission, warned that the people entrusted to manage our super savings – the “trustees” of super funds – are obliged to act in the best interests of fund members but they operate in an opaque system, “surrounded by temptation” to mishandle our savings.

“What happens when we leave these trustees alone in the dark with our money?” he asked.

What was revealed this week?

National Australia Bank executives gave testimony for nearly four days, and their evidence was so appalling it prompted NAB’s chief executive to issue a public apology.

The commission heard the corporate regulator had accused NAB last year, during private correspondence, of more than 100 potentially criminal counts of breaches of its licence in relation to charging fees to super customers for services not provided. The commission also heard fees were deducted from super accounts belonging to NAB customers who had died.

NAB’s lawyers tried repeatedly to prevent damaging documents being disclosed to the public in the hearings, but they were unsuccessful.

The commission also heard how unhelpful NAB’s legal team had been in the lead-up to this round of hearings when it came to producing documents.

NAB is currently paying more than $100m in compensation to super customers who were charged a “plan service fee” for general advice when they did not have an adviser linked to their super account.

Was NAB the only institution in the witness box this week?

No.

On Thursday afternoon, the commission also heard from Ian Silk, the chief executive of Australian Super, the country’s biggest super fund.

Silk’s testimony was highly anticipated. Critics of Australian Super had been hoping the commission would scrutinise the fund’s decision to spend $2m of its members’ fees to establish the online publication the New Daily, and its decision to fund an advertising campaign in March last year, called “Fox and Henhouse,” which attacked the major banks’ lobbying efforts in Canberra.

Silk was unrepentant for both things.

He said the ad campaign was directed at Senate crossbenchers in federal parliament to warn them about the major banks’ attempts to overhaul the default super fund system to make it easier for for-profit super funds to get more members by default.

He said it was a public policy issue and the ad served the interests of Australian Super’s members – and the commission did not criticise him for it.

On Friday, the commission also heard witnesses from IOOF Investment Management Limited, and Energy Super Fund.

What did we learn from this week’s hearings?

We learned that Australians need to become more engaged with their superannuation, for one.

Australians lose billions of dollars each year from their super savings through fee erosion, and from being members of poorly performing funds.

Hodge told the commission that 40% of Australians hold more than one super account, and the multiplicity of accounts gives rise to duplicative administrative costs and multiple unnecessary insurance policies.

Of people with insurance policies linked to their super accounts, more than 20%, or around 2.5m people, have two or more accounts with insurance cover.

Oftentimes people don’t know they are paying for an insurance policy, but the insurance premiums deducted by fund trustees from member accounts are a key driver of balance erosion and can reduce low income earners’ retirement balances.

So what happens next?

The royal commission’s investigation of the super industry continues next week, so we’re not done yet.