Speaking earlier at the Financial Times Digital Media and Broadcasting conference in London, he called on the BBC Trust to ensure the proposals to create a second public service broadcaster "go further".
Duncan said he was encouraged by the ongoing partnership negotiations between Worldwide and Channel 4. However, he believed the current proposals did not "yet represent demonstrable value or a sustainable solution".
Duncan said: "To be blunt, the scale of what the BBC has so far offered the industry in terms of partnership is not sufficient. The BBC has enough resource to do more without damaging its own capacity to invest. Not just Channel 4. But children's; regional news; online; radio. This is not about plundering the BBC to bolster the profits of private shareholders. It is about bolstering a healthy domestic content base."
He added that an unintended gap had grown up between the BBC's annual licence fee income - estimated at £3.6bn in 2009 - and UK TV ad revenues, which have traditionally kept up, but were now forecast to be up to £1bn less than licence fee income this year.
Duncan urged the BBC Trust to ensure the BBC's partnership proposals go further before the system is damaged beyond repair.
Responding to earlier criticism from BSkyB, who reacted to Lord Stephen Carter's call for input into the future of PSB by suggesting Channel 4 had wasted £270m on poor investments, Duncan called the pay-TV broadcaster's suggestions to transform its free-to-air digital channels - E4, More4, Film4 and 4Music - back to paid-for, as "self-serving".
He added: "It's like ITV suggesting that Channel 4 should stop selling advertising. Massive benefit to our competitors. The opposite for viewers".
In a statement issued earlier today by the Channel 4 board, Duncan, who currently earns a package worth £895,000, will now see his wage drop to less than £600,000 a year. He will also give up half of his £450,000 incentive payments which he receives in July, with no proposed new plan in place from August moving forward.
Kevin Lygo, director of TV and Content, has also forfeited 25% of his wage from £772,000 to £575,000. His package doesn't include incentive payments.
Andy Barnes, sales director and Channel 4 board member, isn't expected to have to forgo any of his salary, as his basic is lower and the rest is based on a bonus scheme.
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