John Key's right-hand man is living it up with big-spending lobbyists in the casinos of Las Vegas, sparking questions about their influence on Government policy.

The Prime Minister's chief of staff, Wayne Eagleson, has spent the past week enjoying a shootin', smokin' and boozin' trip to "Sin City". He has been travelling with NZ Post chief executive Brian Roche, and lobbyists Mark Unsworth and Roger Sowry - a former National Party deputy leader who remains a member of John Key and Bill English's inner circle.

The four have dropped "a ton" on blackjack, visited a gun shop where they could shoot an AK47 and dined at a restaurant on The Strip where 50g of caviar costs $500.

The Herald on Sunday has been told Key has explicitly discouraged his ministers from publicly fraternising with lobbyists - but it seems this does not apply to Eagleson.

Key is on holiday himself and did not return Herald on Sunday calls yesterday. But Lesley Hamilton, his spokeswoman, said he was aware of his chief of staff's trip with the lobbyists.

"Wayne Eagleson is on annual leave with a group of long-time friends in the United States. This leave was approved by the PM and this private holiday was funded by Mr Eagleson," she said.

A source close to senior National Party figures expressed surprise that Key would allow such a trip, saying he had always told his ministers not to be seen with lobbyists.

Eagleson, the source said, was "more powerful than a minister".

Otago University political science lecturer Bryce Edwards said the role of chief of staff was vitally important: "Few people know anything about Wayne Eagleson and what he does, but the job description of the chief of staff is pretty basic - these are the people who are supposed to stop controversies like this happening."

Labour leader Phil Goff said the trip raised questions over how the entertainment was being funded: "I've no idea who's paying for what over there."

Goff said fraternisation between lobbyists and Government figures risked giving the impression that access to Government was for sale. "There needs to be caution to ensure that these relationships don't lead to special treatment for the lobbyists' clients."

News of the trip comes from the Facebook updates of the normally discreet Unsworth.

He wrote that the party engaged in "serious betting" on casino blackjack tables before hitting a bar famous for bartop-dancing waitresses.

"It's 12:30am Sowry just did a ton on the tables tonight but he's well up, I am about 10 in front and as Wayne says that doesn't count the free drinks or being able to smoke cigars inside with a Heinie as you bet.

"We had a great night tonight and pushed on to Coyote Ugly and a duelling pianos bar where we all sang Bohemian Rhapsody."

The party is believed to have dined at the pricey Eiffel Tower restaurant where mains cost around $80 and 50g of caviar sets diners back $500. "Our most expensive meal, but great grub," Unsworth said.

The week-long holiday also included a helicopter flight to the Grand Canyon and a meal at an Italian restaurant in San Francisco, which Unsworth said came personally recommended by Key's wife Bronagh.

Unsworth is one of the founders of lobbying firm Saunders Unsworth and is regarded as one of the most influential backroom operators in Wellington.

On its website, his firm takes credit for excluding clients from the costs of climate change policy, protecting the televised advertising of pharmaceuticals, and - somewhat appropriately - blocking tougher casino regulations.

National Party pollster and conservative blogger David Farrar said the success of the firm was due to the lobbyists' close relationship with politicians.

"They're successful partly because they're so well connected."

Roche was picked to head NZ Post in October last year and is believed to receive an annual salary of $1,180,000.

Sir Jim Bolger, chairman of NZ Post, said he was "very relaxed" about the trip because he knew all the parties involved. "Wayne worked with me in the Prime Minister's Office, Sowry was a member of my cabinet, and Wayne and Brian have been friends for years."

Sowry is, in addition to his lobbying work, is a member of the Electricity Commission.

After a long Friday night of free drinks, Unsworth posted online: "Off to the Hoover Dam tomorrow and I think I am the designated driver which is a worry. Still, then we can put the whole trip down as a business expense to the Electricity Commission, no?"

Electricity Commission chairman David Caygill said he was not aware of any official business being conducted in the United States by Unsworth or Sowry, and the line seemed to be in jest.

Actually claiming taxpayer money for a Las Vegas jaunt would be no laughing matter, he said.

The four did not return messages - but according to Unsworth's posts, they're off to Venice Beach in LA today.