Early on in the campaign, National announced it would upgrade 10 single lane bridges and Mr Key said more announcements were expected. However, none have followed other than a re-announcement of rural broadband policy.
Mr Key said it had pulled plans for some other promises, but would deliver them after the byelection. He blamed the media for that.
"On balance we decided there were a few things we wouldn't announce - we're just going to do them after the byelection."
That was because of concern the media "would mischaracterise it", he said.
"If I turn up, you say I'm desperate to win. If you don't turn up, you say I'm ignoring the Far North. When we announce policies on infrastructure you say we're trying to bribe people, and if we don't you say we don't care. That's politics."
The ten bridges policy was derided as 'pork barrel' - an attempt to persuade voters by throwing money at the byelection.
In the 3News Reid Research Poll this week, about three quarters of voters agreed it was a bribe. Mr Key said there would be 'promises' around New Zealand, including Northland. Some would be in the Budget in May.
Mr Key defended the bridges announcement, saying if National had not made any concrete promises, it would have been criticised for taking the electorate for granted.
He said New Zealand First leader Winston Peters had made a raft of promises, from ports and rail to free ferry travel for Super GoldCard holders, "none of which he'll ever complete". However, he had not faced the same scrutiny.
"So it's ok for him to campaign, but we should campaign with one hand behind our backs? You can't have it both ways."
Two polls this week put NZ First leader Winston Peters between 15 and 20 percentage points ahead of National's Mark Osborne.
Mr Key was in Paihia and Kerikeri today, saying his main aim was to persuade National's voters to vote.
"It's a big job but I reckon we can [turn it around]. There is a lot of latent support for National, but mobilising that support is a big issue."
He said the poll gap was on local issues, rather than a vote of no confidence in National. He did not believe National had let down the people of Northland, but said more could be done and the discontent was a result of "decades and decades" of Northland being behind Auckland.
Mr Peters' campaign has been based on "sending them a message" and Mr Key said National had heard that message.
"The people of Northland are ambitious and want Northland to do better. We hear that message loud and clear. We are not naive about it, we have to share resources right around the country - it can't just solely be about Northland."
He believed National had done a good job of lifting the economy, he said, but more was needed.
- Claire Trevett of the New Zealand Herald
