Helen Clark must explain why she hid from the public her knowledge about Winston Peters' donation from Owen Glenn, says National Party Leader John Key.

"It is apparent from Mr Glenn's testimony to the Privileges Committee today that at least two people at the very top of the Labour Party - Helen Clark and Mike Williams - knew Mr Peters had approached Mr Glenn and obtained a $100,000 donation.

"That is the donation which Mr Peters then proceeded to deny for months on end.

"Helen Clark must explain to the public why she did not come clean with the country earlier.

"She must explain why she allowed her Minister to continue to deny all knowledge of the donation when she knew from Mr Glenn that one had been made.

"She was also aware from Mr Glenn that Mike Williams knew back in 2005 that Mr Peters had sought the donation and that it had been made.

"The public are owed a comprehensive explanation from Helen Clark about Labour's deep involvement in this saga."