Watch: Explosive claims of former Russian spy who says he was harassed by Kiwi police and poisoned in Auckland

There is more to the incredible tale told by a former Russian KGB agent who appeared on UK TV today claiming he was poisoned 10 years ago on Auckland's Queen Street, as an in-depth investigation by TVNZ1's Sunday found out during an exclusive 2007 interview with him.

Boris Karpichkov arrived in Auckland in 2006 on a fake Lithuanian passport. He then claimed he was followed and physically assaulted by the New Zealand police and members of the NZSIS.

Mr Karpichkov admitted being a former Russian spy, but said he wasn't in active service when he came to New Zealand to try and find a safe haven for himself and his family after receiving death threats while living in London.

He told TVNZ1's Sunday that he turned in his fake passport 12 days after arriving in the country in a bid to try and be transparent so he could claim refugee status. The Department of Immigration then returned his knowingly fraudulent document with a stamped work permit on it allowing him to stay.

From there he says things became like something out of a Hollywood spy movie, as he noticed cars began to track his movements.

"You can consider me insane, or obsessed and paranoid but it's an established fact and can be proven," Mr Karpichkov said.

1 NEWS has more interesting details about the double agent's life. Source: 1 NEWS

The ex-spy photographed the vehicles and even confronted a man he believed to be following him which led to an altercation.

"I told him enough is enough and took his picture, the guy then jumped out the car and kicked and punched me yelling 'I will smash your f***ing phone and head'," he told Sunday's Janet McIntyre.

Mr Karpichkov reported the assault to the police but heard nothing back from them until two months later when Detective Seargent Mark Williams called him and admitted it was a police officer that had assaulted him and tried to discourage him from taking the matter further.

His phone conversations with Detective Williams were recorded by Mr Karpichkov for evidence and played back to TVNZ1's Sunday.

One of the calls had the detective reading out a letter which was oddly written as if Mr Karpichkov had authored it himself and accepted an apology from the officer who assaulted him so the matter would go away.

He accepted the apology hoping it would end his surveillance, but says after a brief lull he began to be followed again. Shortly after this Mr Karpichkov said he came down with a mystery illness that doctor's couldn't identify.

Mr Karpichkov says he lost 20kgs and believes he was poisoned by a Russian agent, similar to the claim which he made on British TV today.

He eventually lost his fight to stay in New Zealand in October 2007 due to historical links to organised crime in Russia and Latvia, which he denied, saying he was not an active spook and was never involved in crime.

He once again used his fake passport to leave the country and was given no troubles at customs.

The NZSIS released a statement to 1 NEWS today, with a spokesman saying: "At the time it was confirmed to media that Mr Karpichkov had been in New Zealand, and that his KGB background was known."

The NZ Police told 1 NEWS they're examining what information they hold on Mr Karpichkov but due to the cases historic nature "it's likely to take some time".

TVNZ1's Sunday did an in-depth investigation into Boris Karpichkov's stranger than fiction story in 2007. Source: Sunday