EVEN if Tony Abbott were caught streaking naked down Collins Street in Melbourne the Coalition would probably still win the looming election, former Federal Treasurer Peter Costello says.

The nation's longest serving Treasurer is tipping victory with a "large majority" for the Coalition on September 14.

But this boast from a Liberal elder won't be welcomed by the current leadership team struggling to keep the lid on expectations.

In an interview ahead of being made a life member of the Liberal Party this evening , Mr Costello talks to News Limited about the difficulties facing the next government in returning the budget into the black, the Coalition's prospects at the ballot box and his tumultuous relationship with former Prime Minister John Howard.

The Coalition has lifted its game in recent months but it is still too early to tell if an Abbott-led government would have the reforming zeal needed to revolutionise the nation's tax system and put it on a more sustainable footing, he claims.

"The (broken) promise to have the budget in surplus has been quite catastrophic for Gillard," Mr Costello said.

"Unless Tony Abbot gets caught stark raving naked in Collins Street, I think it's over and even then he might win."

The Coalition's decision to postpone the planned increase in the superannuation contributions to 9.5 per cent for two years was welcomed as a good first move as it will deliver "big money" to the nation's bottom line over the coming financial years.

The key advice from the last Treasurer to deliver a budget surplus - 10 surpluses out of 12 budgets - to shadow treasurer Joe Hockey was to get spending under control.

The Gillard government's centre piece - the Gonski education reforms - are blasted as a "pie in the sky" promise that will lift spending but not necessarily educational outcomes.

Mr Costello is also critical that while the National Disability Scheme is a worthy project, the funding of the national roll-out in 2018-19 will be enormously expensive.

But he defended the axed Baby Bonus scheme - one of his signature decisions while Treasurer - as being the right thing at the time, even if the introduction of the much more generous paid parental leave was the beginning of the end for the program.

Mr Costello said that after 19 years in parliament and more than 13 years as deputy leader it was "pleasing" to become only the fourth person to receive honorary life membership of the Federal Liberal Party.

The award was first given to John and Janette Howard and former Victorian MP and state president David Kemp last year.

But Mr Costello seems prouder of his legacy in terms of former staff members who are part of the next generation of Liberal leaders.

His alumni includes Victorian Treasurer Michael O'Brien, Federal MP Kelly O'Dwyer - who succeeded her former boss as the member for Higgins - and Victorian Federal Senators Mitch Fifield and Scott Ryan.

Despite sitting beside him in cabinet for 12 years, Mr Costello admits not being disappointed about former PM John Howard's decision to miss the gala dinner at the Melbourne Museum.

"I don't spend a lot of time with him," Mr Costello said.

"I advised him that it would have been in his interests and the interests of the Liberal Party for him to stand down. And I think history confirmed I was right. He lost his seat."

"I don't think he liked that advice but I think it was the right advice for him and the Liberal Party and he knows that. He is not the kind of person to say sorry but he knows that. So you let bygones be bygones. I don't have to remind him of it."

Mr Costello is also upbeat the Victorian Liberal Party is moving in the right direction since the dumping of former Premier Ted Baillieu.

"Napthine has made a very good start. The public response to Napthine has been very good and that has turned Victoria's fortunes quite a bit at a federal level," he said.

Mr Costello also credited the Opposition's move towards major issues such as the economy has also played a key role in lifting the Coalitions' support base, especially in states such as Victoria.

QUOTABLE QUOTES

Getting the budget back in the black:

"We need a full court press. And we have got to stop the increases in spending."

Telling John Howard to step down

"I don't think he liked that advice but I think it was the right advice for him and the Liberal Party and he knows that. He is not the kind of person to say sorry but he knows that."

Gonski education reforms

"Gonski is pie in the sky stuff with massive big increases. It is not a question of less money going into schools. But spending doesn't need to be increased as much as recommended."

This year's budget

"By and large the people that will benefit are the high income earners. It will be harder on poor families and much more generous to middle and high income earners."

Liberals in Victoria after Ted

"There has been a big turnaround. Napthine has made a very good start. The public response to Napthine has been very good and that has been reflected in the polls and turned Victoria's fortunes quite a bit at the federal level,"

NDIS