Do we need a Royal Commission on the public service?

The Labour Party has announced that it would establish a Royal Commission to inquire into the public service. This arises from concerns about threats to the political neutrality of public servants. It would look at whether pressures from ministers have interfered with public servants' willingness to give 'free and frank advice' and whether there are growing risks of corruption.
The present Minister of State Services, Jonathan Coleman, has written this proposal off, however, claiming that it would be 'wasteful' and that it was unnecessary as both National and Labour have recently supported amendments to the law on the state sector and public finance. These amendments were significant, but they do not really address the concerns that Labour's spokesperson, Maryan Street, was raising. There are still genuine concerns surrounding the behaviour of ministers towards public servants and the extent to which this may compromise the political neutrality of the public service and its willingness to offer free and frank advice, as opposed to simply telling ministers what they want to hear.
There's a fine balancing act for public servants. They tend to be better informed than the average citizen about political life, and of course they have their personal political opinions. And yet they are required to act as professionals in a way that is politically neutral. This means that they should serve the government of the day loyally, regardless of their personal views. At the same time, they should be able to offer advice to ministers that evaluates all options. Advice that conflicts with what the government may prefer should not be withheld out of fear of courting displeasure. Public confidence in public services and in policy development relies on our being able to trust that ministers get to hear the whole story (and not just carefully edited highlights) from their advisers. There have been some scandals recently emerging out of Wellington that raise strong suspicions that 'free and frank advice' is no longer welcome in the Beehive.
As for corruption, New Zealand is ranked by Transparency International as the least corrupt country on earth. But no-one seems to know how we got to that position, and it certainly gives us no cause for complacency. Maintaining a relatively clean record in the public services is vital, and we could do with a close examination of what works and what doesn't.
So, yes, a full commission of inquiry into these questions would be great idea.