A broad national interest override risks a "conga line of lobbyists" pressuring ministers to leverage it to exempt development, warns the author of the audit behind Labor's nature law overhaul.

Graeme Samuel, who penned the now five-year-old review of the federal environment protections, says the national interest exemption is too open to interpretation and at risk of legal disputes and exploitation by ministers.

"Also, the risk to the minister is there'll be a conga line of lobbyists that will be outside their door saying, 'Well, look, you just use the national interest exemption'," the former consumer watchdog chief warned at a parliamentary hearing in Canberra.

The national interest override has been included in the Environment Minister Murray Watt's overhaul of the Environment Prote

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