Opposition party leaders are outraged they've been pre-registered to buy shares in Mighty River Power, but the Government has suggested it is a political stunt.

Labour leader David Shearer and Green Party co-leaders Russel Norman and Metiria Turei all received notification emails over the weekend telling them they had been pre-registered to buy shares.

The registration process opened last Tuesday and does not compel people to buy.

Norman said he had contacted Treasury to cancel his registration but was disappointed by its cavalier attitude.

Shearer said his registration proved the system was "shonky".

But Acting Prime Minister Bill English said he was confident the nearly 300,000 people pre-registered were genuine.

He suggested the registration of  the leaders was a political stunt by the parties involved.

"Maybe it's not a co-incidence that on the day the asset sales petition is being presented, the leaders of the opposition parties funnily enough find themselves pre-registered. I wouldn't be surprised if it's a stunt."

And the system was secure enough, he said.

"You can't stand by every computer screen in the country to see what people are putting on."

Being registered was a long way short of having to buy shares, English said.

Shearer found out he had been registered twice, likely as a political joke, including once under the name "DonKey".

His parliamentary email address was used which meant he became aware of the stunt.

It was possible his name had been entered more times under a different email address.

"If someone can sign me up without my knowing then there's the opportunity for many others to be signed up as well - who knows how many people are going to be on that register that are not actually bona fide."

Norman and Turei had also been signed up and only found out when emails arrived in their parliamentary inboxes.

They raised the matter with Treasury and were not satisfied with the suggestion the registration was simply made in jest.

Shearer said the registrations in his name showed how "shonky" the process was.

"Whose dog and cat and next-door neighbour is being signed up without them knowing?"

He said he wanted to alert people to the fact that their name may be inadvertently entered.

It was too early to say whether he would take action to pursue those who had registered him.

"We'll be following that up and making some further investigations about how that can come about."

Shearer said he never had any intention to purchase shares in the state-owned energy company when the Government sells it later this year.

- © Fairfax NZ News