Mental health and addiction services are expected to receive a massive funding boost of well over $1 billion when Grant Robertson's long-anticipated Wellbeing Budget is unveiled today.
It will also be the first Budget which reports on the reduction of child poverty, by law.
But National is planning to steal some of the Government's Budget Day thunder by revealing today how it came by secret Budget documents earlier in the week.
The Government's response to what has been called a crisis in mental health services has been slow.
Prime Minister Jacinda Ardern yesterday outlined the Government's response to the inquiry into mental health and addiction which reported in December, but kept funding decisions under wraps.
She said delivering services to meet mild to moderate mental health and addiction needs would be "transformational".
Mental wellbeing is one of the Government's five priorities for the Budget – with a special focus on under-24-year-olds.
The priorities were unveiled in December last year, as were the outlines of what to expect from a Wellbeing Budget.
But after a steady build-up to one of the most anticipated Budgets in many years, suddenly it became one the least anticipated, following a Budget leak this week.
Revelations on Tuesday that National had acquired sensitive Treasury information on at least 19 out of 40 Budget areas of spending threw Treasury into a security panic.
Treasury's decision to call in the police and Robertson's call to National to stop releasing any more Budget secrets infuriated National which rejects any suggestion of unlawful activity.
That has led to a toxic political atmosphere leading into today's Budget.
Robertson, who will be delivering his second Budget today, spent less time promoting the Budget at Parliament yesterday and more time discussing the leak.
National's finance spokeswoman, Amy Adams, said the Budget revelations had taken the focus off the Budget and people were now talking about the inability of the Government to run a Budget process.
"When we were able to obtain Budget information that we should never have been able to obtain, of course that's relevant," she told the Herald.
"Our job is to highlight weaknesses of the Government. We think this is a significant failing of the Government and we also think it makes a mockery of their claim to be prioritising wellbeing and some of the spending choices we were able to see."
People were focusing on what was "a shambles" rather than the big reveal.
Adams has been critical not so much of the wellbeing theme of the Budget but the notion that this is the first time that Governments have made Budget decisions based on outcomes, and based on evidence.
Robertson has said that wellbeing "means people living lives of purpose, balance and meaning into them, and having the capabilities to do so".
All Budget bids had to go through process that argued why it would improve wellbeing and further the Government's priorities, which are:
• Creating opportunities for productive businesses, regions, iwi and others to transition to a sustainable and low-emissions economy;
• Supporting a thriving nation in the digital age through innovation, social and economic opportunities;
• Reducing child poverty and improving child wellbeing, including addressing family violence;
• Supporting mental wellbeing for all New Zealanders, with a special focus on under-24-year-olds; and
• Lifting Maori and Pacific incomes, skills and opportunities.
The Government's priorities themselves are more oriented towards social issues than National's which put more emphasis on the economy.
National's priorities in 2017 were to: responsibly manage the Government's finances; build a more productive and competitive economy; deliver better public services within tight financial constraints; and rebuild Christchurch and respond to the Kaikōura earthquakes.