"I've apologised to the Electoral Commission and to the National Party. I've accepted full responsibility and we're in the process of waiting to see what happens," Mr Walford said.
"The authorisation statement hadn't been put on. It had been printed but it had been omitted when they did the job [of applying the signage to the ute]. I didn't check."
A spokesman for Police National Headquarters said a referral from the Electoral Commission in relation to the matter had been received and was being assessed.
Mr Walford said he "had a pretty good idea who it was" who lodged the complaint, which included a photo taken on June 25, the day he attended a meeting of Hawke's Bay Regional Council, where councillors voted to support investing up to $80 million in the Ruataniwha dam.
Mr Walford's two main political rivals yesterday denied any involvement in the complaint to the Electoral Commission.
Labour's Napier candidate, Stuart Nash, said: "It's not me at all. I have no interest in what Wayne does and what Wayne doesn't do. We have got a very clear strategy of what we want to achieve and we're focusing on implementing that strategy."
Napier Green Party candidate Paul Bailey said: "To the best of my knowledge it had nothing to do with us."
Meanwhile, in the neighbouring Tukituki electorate, Labour candidate Anna Lorck said sitting MP Mr Foss' family holiday in Hawaii last week shows he's "too relaxed" about the election. Mr Foss denied the claim,but said his family always came first.
Ms Lorck said Mr Foss was "lying back in his deckchair and drinking pina coladas" on the tropical island while she was busy on the campaign trail.
Mr Foss confirmed he had spent "a good week" with his family at Waikiki Beach in Honolulu, Hawaii, up until Wednesday, July 16.
"We had a family holiday."
However, he denied the holiday showed he was too relaxed about the upcoming election.
"I work hard for Hawke's Bay families and I am backing the Bay each and every day.
"So much for Labour's pledge to not be nasty."
Politicians' holidays have been subject to scrutiny as David Cunliffe was slammed for taking a three-day skiing holiday in Queenstown, despite Labour's languishing in the polls, and Prime Minister John Key spent 10 days in Hawaii.
Mr Foss said he hadn't rubbed shoulders with Mr Key, who returned to New Zealand on Sunday.
"I never saw him ... we see enough of each other down here [in Wellington]."
Mr Foss and Mr Key had, however, talked casually about "what a wonderful climate Hawaii was" since their return.
Ms Lorck said while Mr Foss was in Hawaii, she had participated in The Ice Challenge, in which community leaders were dunked with icy water to raise money for cancer sufferers, organised by Flaxmere councillor Henare O'Keefe.
"Old Craig was lying back in his deckchair drinking pina coladas while I was in Hastings, getting frozen in The Ice Challenge for my electorate.
"I don't expect anything less than Craig to put up his feet.
"I think he's [Mr Foss] too relaxed about it. He's said publicly he doesn't need to campaign."
However, Ms Lorck said "it's important for any dad to spend time with his children".
Ms Lorck had spent two days with her husband and two of their girls in Rotorua on Thursday and Friday last week.
During the trip she spent time "on the campaign trail", with Rotorua Labour candidate and former TV presenter Tamati Coffey and Labour MP Phil Goff.
