New Zealand obtained secret communications intelligence about the Soviet Union that was key to ending the Cold War, former Prime Minister David Lange has revealed.

Mr Lange yesterday said security laws might prevent him from ever disclosing the full details, but as Prime Minister he oversaw the gathering of intelligence that was very useful to the Western bloc’s negotiating position.

"I facilitated New Zealand becoming a receiver of intelligence that they [the Eastern bloc] did not wish to be in our hands, and that limited the ability of the Eastern bloc to communicate with each other."

This was despite the fact that Mr Lange’s nuclear-free law put relations with the United States on ice, and endeared him to Eastern bloc nations.

"‘Broker role is not the right word. It wasn’t involving a consensual activity. It involved one-sided activity which provided the other side with what they wanted. It was no use to us."

He made light of his involvement in the intelligence-gathering world - "I look ridiculous in a trench coat" - but emphasised the information gained was in the interests of the Western bloc.

"I’ve stayed quiet about some amazing things while other people talk the most extraordinary tripe," he said, referring to the hoaxers who recently claimed to have spied on Maori politicians for the Security Intelligence Service.

He had known two of the "spies", Jack Sanders and Gerald Thorns. Mr Thorns had managed to get his photo taken with Mr Lange, which Mr Lange feared would have been used in subsequent subterfuges.

Mr Lange’s memoirs are due to be published by Penguin in September, and he was upbeat in working to complete them, despite ill-health due to kidney failure.

"I’m on dialysis about 10 hours a night. My kidney function is gone, but the rest of me is good. I’m good in the morning, a bit of a zombie in the afternoon."

Though no longer active in politics, Mr Lange he had views on New Zealand’s constitutional future.

"Prince Charles’ visit to New Zealand attracted less attention than Shrek, the sheep. That’s a sign that things are changing, and it’s a sign that we ought to heed."

But his support for a republic was tempered by concerns about what form it would take.

"If we could have a republic without a president, I’d be all for it.

"It simply seems to me to be an unnecessary appendage."

He did not support United Future leader Peter Dunne’s bill proposing that Waitangi Day be renamed New Zealand Day, as in the 1970s.