Former Labor government minister Peter Garrett says he stands by his tough criticism of former prime minister Kevin Rudd, including describing him as a megalomaniac.

Mr Garrett makes the assessment of the former Labor leader in his biography Big Blue Sky, which is set to be released on Wednesday.

“I’m not the only one to think it either,” he told the Seven Network’s Sunday Night program.

• Turnbull deplores Turkey terror
• The dangerous policy the government dares not mention

It’s not the former Midnight Oil frontman’s only criticism of Mr Rudd, who demoted him as environment minister after the government’s failed pink batts scheme.

Mr Garrett says in his book that supporting Rudd in light of his “trail of destruction and abandoned policy” was his biggest mistake in nearly 10 years in parliament.

“I’ve been particularly strong in this book about leadership and Rudd’s leadership and I think it needed to be said,” Mr Garrett told the program.

“Rudd wasn’t someone who was easy to work with in that way, and his vanity and his exercise of power as prime minister was contrary ultimately, to me, to what good leadership is.”

Mr Garrett also addressed his changing story about an envelope of cash given to him by poker machine interests, saying it was actually a cheque that he returned.

He denies the money was a bribe.

“I’ve never said it was and I’m not saying it under any pressure,” he said.