Key Points:

Winston Peters has owned up to a cash donation - but only after his hand was forced by the Serious Fraud Office.

A $40,000 gift from the Spencer Trust was Mr Peters' one amendment to the Register of MPs' Pecuniary Interests when it was released yesterday.

This was the donation the SFO uncovered and handed over to Parliament's privileges committee last month.

It covered the $40,000 court costs Mr Peters was ordered to pay after his unsuccessful election petition against National's Bob Clarkson in 2005.

The SFO's evidence contradicted the explanation Mr Peters and his lawyer Brian Henry gave to the committee about how the $40,000 debt was paid.

Mr Henry at first told the committee he paid the costs. Mr Peters told it he believed he paid.

Mr Henry then clarified in writing that he paid but Mr Peters reimbursed him shortly afterwards and Mr Peters backed up this version in a speech to Upper Hutt Grey Power.

But Mr Peters' amendment yesterday read: "Cash donation towards Tauranga electoral petition costs - Spencer Trust."

Parliament's Deputy Clerk Debra Angus said: "Mr Peters has advised the Registrar that there are no other donations or gifts that require any declaration on his part for the years 2006, 2007 and 2008 beyond what has been disclosed already."

Mr Peters had to submit amended returns for 2006, 2007 and 2008 after Parliament upheld the committee's finding he knowingly provided false or misleading information by not declaring a $100,000 donation from billionaire Owen Glenn on the register. Mr Peters has already amended the return to include Mr Glenn's donation.

SFO director Grant Liddell's decision to go to the committee was criticised by Mr Peters, Prime Minister Helen Clark and Deputy Prime Minister and Attorney-General Michael Cullen.

The SFO uncovered the donation during its separate investigation of the Spencer Trust, which funnelled $234,171 towards the benefit of NZ First from 2005-2007. The $40,000 is the first amount officially declared.

Mr Liddell told the committee he believed it had been misled and he approached it after considering "my responsibility as head of a law enforcement agency where I have information that is relevant to the possible breach of the laws of New Zealand".

Mr Liddell said the $40,000 was not declared on the register and was therefore a breach of Parliament's standing orders, which were part of the laws of New Zealand.

The committee's report said it was surprised to get the SFO evidence after the explanation from Mr Peters and Mr Henry.