Turnbull has proposed an independent committee to handle compliance, reporting and transparency. The committee will be comprised of an audit expert, the president of the Remuneration Tribunal, a formal judicial officer, and a former member of parliament, and will be accompanied by monthly disclosure of expenses in a searchable database.

While this may result in fewer egregious transgressions – such as chartering a helicopter for an 80-kilometre flight to a party function – it is unlikely to address the broader issue of politicians' entitlements at all.

The key problem with Turnbull's plan arises when he says that politicians' expenses are no different from business expenses in the private sector. There are several important reasons why this is not true, and it is these differences that undermine the current system and will bedevil Turnbull's committee.

The differences start at the most basic level. There is no checklist of what makes a good minister: no real KPIs or targets that can be set or measured. In the private sector, yardsticks are typically obvious: a salesperson is measured against their sales targets, a lawyer against their billing, inventory managers are measured against the efficiency of their supply network. Their success, and that of the organisation as a whole, is measurable.

Businesses routinely compare the cost of expenses against the level and likelihood of the benefits they would generate. But how do we assess the performance of the Minister for Health for example? Basically it comes down to whether the stakeholders in the industry, the general public and your colleagues in parliament think you are doing a good job.

In practice, this means ministers who are regularly in the media, gladhanding around the country, and spending money are successful. However it also means, should a politician want to be in a particular location for personal reasons, they can essentially manufacture legitimate business anywhere in the country.

In private businesses, issues over expenses can be resolved by clear lines of authority: staff report to bosses, who report to the CEO, who reports to the board, who are ultimately responsible to shareholders. These are people with the authority to make judgments on the merits of expenses with set budgets – and clear incentives to watch out for waste.

In politics, none of these things apply. The Prime Minister cannot personally oversee all expenses, and the people he delegates authority to are those causing the problems. Far from having the incentive to reduce costs, ministers are rewarded and promoted for maximising their visibility, which means maximising entitlements. There is a reason why all sides of politics are plagued by entitlement scandals.

How can any extra-parliamentary body second-guess a minister's judgment on a line-ball, work-related expense? Specifically, by what right would they rule that announcing government funding for new cancer drugs should not be done in Brisbane? Exactly how many trips to the Gold Coast constitute a misuse of entitlements, and how many are just part of the job?

The point is not whether Sussan Ley was within entitlements or not. The point is that it is almost impossible to reach agreement on what the rules should be in advance – only upon review. After all, the much vaunted pub test is just a retrospective assessment of someone's judgment. A rules-based entitlements system will always be fallible because it operates in a political system that is fundamentally uncertain.

There is no easy solution to this problem, which is why Turnbull has stalled up until now on the issue of reform. Abolish travel entitlements altogether and candidates for foreign minister may suddenly be light on the ground. Setting discretionary budgets risks greenlighting the use of expenses for nakedly political purposes, or turning them into another funding mechanism for the parties.

It's hard to see how Turnbull's committee can resolve this. At best they can assess whether costs to be incurred are reasonable. At worst they simply represent a target for politicians to blame when their travel entitlements cause angst in the media.

Simon Cowan is research manager at the Centre for Independent Studies.