MPs will be debating the perks that some of their predecessors get over the coming weeks.

Retired MPs who were in Parliament before the 1999 election get an international travel fund for themselves and their partner of the equivalent of a return business class trip to London.

An amendment to increase that will be debated in parliament this week.

Prime Minister John Key says it's a technical change and indicates there are problems with the current system.

"It's really just recognising that they wrote in an old law that you'd get the cheapest fare. But like a lot of things in life they might offer three seats and you can never get it on an airline and you can't fly."

Labour leader Andrew Little says he doesn't want it costing taxpayers any more.

"My advice is that it won't generally cost the taxpayer more, it's going back to an old formula that applied that kept the cost at a fairly modest level."

He says it's incumbent on MPs to see that it doesn't cost taxpayers any more than it needs to.

A former MP says they have no say in the decision made on their overseas travel fund.

Tau Henare who qualifies for the fund says they can not influence the decision.

"One day they make a pay increase, the next they take it away. Ex MP's don't really have anything to do with it so we take it on the chin whatever decision they make."

Legal blogger Graeme Edgeler estimates it'll go up from about $11,000 to around $20,000.