Attorney-General Chris Finlayson said yesterday that customary title was "an ownership title" - meaning that Maori groups awarded customary title in the foreshore and seabed will be the legal owners of it and the minerals beneath it.

That makes it quite different to the existing Foreshore and Seabed Act 2004, which will be repealed under the agreement reached on Monday between National, the Maori Party and the Iwi Leadership Group.

In response to Herald questions, he also clarified some of the conditions for getting customary title.

Under Labour's act, legal ownership of the foreshore and seabed was not possible under its equivalent of customary title, territorial customary rights.

Answering Labour's David Parker in Parliament, Mr Finlayson said Maori would see no change in terms of vesting the foreshore and seabed in "public domain", rather than the present Crown ownership.

But the legal situation in getting customary title, a new form of property title, is different.

Foreshore and seabed will be deemed to be in "the public domain" and owned by no one until an iwi or hapu is awarded customary title by a court or the Government, although another term may be found.

The relevant customary title will then sit over the public domain designation in the same way that fee simple title sits over the Crown's radical title to land.

Mr Finlayson said public domain would provide "a staging post" in which some iwi or hapu would be able to investigate customary title.

Mr Finlayson also clarified part of the test by which customary title will be decided.

Iwi will have to prove they have had exclusive use and occupation of the relevant area since 1840.

Mr Finlayson said "exclusivity" was a common-law concept "which requires the applicant group to demonstrate their interest in a particular area is generally akin to ownership in that they are able to exclude non-members of the customary title-holder group".

"Exclusivity must have been continuous without substantial interruption since 1840."

Some examples of interruption included selling the land, having a port built over it or, as in the case of Auckland beaches, having thousands of people passing through and using it and the local iwi not exercising any control over use or occupation.

Mr Finlayson confirmed in Parliament that the holders of customary title, while not able to sell the foreshore and seabed, would own the non-nationalised minerals beneath it - all except gold, silver, uranium and petroleum.

Maori Party MP Hone Harawira, vowed to fight for Maori title over the foreshore and seabed "because it is ours by right".

"And not just customary title either for formal legislative recognition of our rights to the foreshore and seabed, as guaranteed under Te Tiriti o Waitangi and the Declaration of the Rights of Indigenous Peoples," he said.

New Zealand First leader Winston Peters said it was a divisive decision that would lead to a flood of claims and years of infighting in iwi.