John Banks had a team of lawyers advising him on the laws surrounding election campaign donations, police files reveal.

Mr Banks, now MP for Epsom, has criticised the Local Electoral Act as "unclear, unfair and unworkable".

The Government this week announced changes to the law - on the same day police disclosed files from their investigation into anonymous donations to Mr Banks' 2010 campaign to be Auckland mayor.

Millionaire Kim Dotcom, who is facing extradition on United States anti-piracy charges, says Mr Banks solicited the $50,000 gift, which was later registered as anonymous. Police also investigated a $15,000 donation from SkyCity and radio advertising, but said there wasn't enough evidence to press charges.

But sworn statements from Dotcom, his lawyer and bodyguard cast doubts on whether Mr Banks, now ACT leader, was upfront about the donations.

Mr Banks said this week: “How can anyone be reasonably expected to comply with a law that cannot be understood - even by the legal profession?"

But volunteers on the failed campaign, including his treasurer, told police Mr Banks had employed lawyers. "We had a legal firm that advised us on the legislation behind donations and we took advice from them."

Labour's deputy leader, Grant Robertson, said Prime Minister John Key must sack Mr Banks. "Reading the papers, there is a fair degree of thought went into how to hide away who the donations came from. They clearly went out of their way to make them anonymous and they had legal advice to that end."

Mr Robertson has also called on Mr Key to require Mr Banks to make public his witness statement - which had been withheld at Mr Banks' request.

"Given the damning sworn statements from others in the file, Mr Banks needs to be transparent with the public," Mr Robertson said.

The documents also throw into question Mr Banks' claims about a Christmas holiday to Hong Kong.

Mr Banks has always insisted he haggled for a discount on his room at the Grand Hyatt hotel. But Dotcom told police Mr Banks contacted his bodyguard, Wayne Tempero, at the end of last year. "I had told Mr Banks that I had stayed in this top floor of the Hyatt in Hong Kong for six years. It was obvious therefore that I would recommend that hotel and it was clear to me that he was seeking my help in getting him a good rate at the hotel."

Dotcom offered his suite but Mr Banks told Mr Tempero it would be a "breach of the rules" MPs must abide by.

Dotcom said he rang the hotel to tell them Mr Banks was a VIP and should be treated as such.

Mr Banks could not be contacted last night.

- © Fairfax NZ News