Prime Minister John Key is among senior Government figures left red-faced after their staff claimed FlyBuys points when spending taxpayer money.

Aides to 10 high-ranking politicians have been warned twice in three months for claiming loyalty points from money spent on official business.

A study of ministers' expenses by the Herald on Sunday found 19 cases of staff earning personal FlyBuys points over the past year.

It comes after this month's expenses scandal revealed former ministers had spent taxpayer cash on porn movies, massages and luxurious meals.

The latest warning was sent on Friday after Herald on Sunday inquiries and followed an earlier email to remind ministers' staff that loyalty cards "are not to be used when spending taxpayer money".

"This is on the principle that no personal benefit must occur when expending taxpayers' funds," Ministerial Services assistant general manager Richard McDonald said in an email on March 31.

The Ministerial Offices Handbook - a guide to the regulations and laws governing a minister's office - clearly states loyalty points "should not be used for private purchases".

It explicitly says no airpoints or any other loyalty scheme points can be claimed when on ministerial business.

"Please note that this is a principle which applies through the Public Service to any personal benefit accruing from the business activities of the government," it reads.

Those affected by last week's discovery include Key, police minister Judith Collins, conservation minister Nick Smith, trade minister Tim Groser, education minister Anne Tolley and Act leader Rodney Hide.

A spokeswoman for the Prime Minister's office said a staff credit card had been used to buy a $240 bush shirt as a gift for a guest of the Government.

The staff member handed over a personal FlyBuys card to collect points from the sale.

The spokeswoman said: "All ministerial staff have now been reminded of the rules."

The rules were broken by staff from the offices of Customs minister Maurice Williamson and defence minister Wayne Mapp four times each.

The same FlyBuys card was used with four purchases from Williamson's office.

Four different cards were used by Mapp's staff. There were two cases from the office of associate health minister Jonathan Coleman - with the same card used to claim points from purchases.

Most of the 19 purchases were made at the New World supermarket close to Parliament, and include beer, wine and food for functions in Ministers' offices.

In some cases, staff saved the taxpayer money - offering coupons to get discounts.

In Hide's office, the staff member who shopped for the office Christmas party spent $739 - then used coupons to cut the cost by $151.

Spokesmen for affected offices confirmed the claims. Most said they were made in error and staff had been reminded of the rules.

Smith's spokesman said the relevant staff member would be asked to arrange for the FlyBuys points to be deducted from their loyalty scheme.

A spokesman for the Department of Internal Affairs - which runs Ministerial Services - said collating ministerial credit card and expenses records under the Official Information Act had identified the practice of staff claiming FlyBuys points.