Prime Minister John Key says he does not use the MPs travel perk to take his wife Bronagh overseas, but only because his personal wealth means he can afford not to.

Mr Key yesterday appeared powerless to stop ministers sidestepping his directive that they do not take their partners overseas with them in order to reflect the tough economic times.

Ministers Rodney Hide, David Carter and Peter Dunne have all circumvented his edict by keeping their partner's travel off the ministerial tab, and billing them to their separate parliamentary perk instead.

Mr Key pays for Bronagh even though she is largely accompanying him in an official role.

"I think it would be difficult for me to justify with my independent financial means that the taxpayer should pay for me to take my family on holiday," he said yesterday.

He did not take "lots of things", such as the perks of a fuel card or self-drive car.

But Mr Key stopped short of saying the partner's travel perk was unnecessary, as circumstances were different for other MPs.

"You don't want 120 members of Parliament who have the financial independence to be able to make the financial decisions that I make. It wouldn't be the House of Representatives, we need people from all walks of life."

Mr Key is only responsible for Ministerial Services, not Parliamentary Service which administers the partner's travel perk of up to a 90 per cent discount on flights.

Mr Key said it was up to MPs to decide whether to use it to take their partners overseas, but they had to be aware the media would report it and the public would judge under the recently opened expenses regime.

"I'm saying it's up to each member to decide and consider the consequences of media intrusion if they do."

As of last night, two National ministers - Maurice Williamson and Judith Collins - were refusing to respond to Herald queries about their travel bills over winter. Mr Williamson, the Minister of Building and Construction, spent $13,414 on international ministerial travel and $10,984 on his perk - a total of $24,398.

Ms Collins, Minister of Police and Corrections, spent $20,283 on international travel and $5417 on her perk - a total of $25,700.