Outsourcing the Commonwealth public sector is not like the steamy box-office hit Fifty Shades of Grey, a senior Canberra bureaucrat has warned.

And the Abbott Government's "contestability" agenda was at risk of getting tied up by departmental managers too "risk-averse" to make the first move, the boss of the new Shared Services Centre told a gathering of public servants in Canberra on Tuesday.

In a rare attempt to make shared services sexy, Delaine Wilson said departments must share the power with the outfits hired to do their outsourced work, in contrast to the relationship enjoyed in Fifty Shades by millionaire bondage enthusiast Christian Grey over his young lover Anastasia Steel.

But the Shared Services chief executive does want someone to take control, warning that managers across the bureaucracy will be slow to embrace the new era of outsourcing their non-core functions without a little coercion.

Nor was Ms Wilson shy about cracking the whip with some of the home-grown shared services operations springing up around the public service, arguing there was no place for small fry if contestability was to succeed.

But the key message was that everyone had to feel they were in control if this thing was going to work.

Ms Wilson said it was important to develop a "strong spirit of collaboration backed up by governance arrangements which respect the interest of providers and receivers of services".

"This governance arrangement ensures the genuine creation of partnerships and not submissive relationships," she told the Institute of Public Affairs conference in the capital on Tuesday.

"It's not Fifty Shades of Grey here, it's actually about a genuine partnership - it's not easy to achieve."

The push for departments to outsource or privatise non-core functions is gaining pace. "Portfolio stocktakes" are under way with government departments being assessed to see if work can be farmed out to either the private sector or the SSC.

Ms Wilson, whose Shared Services Centre has grown to 600 public servants, already larger than several departments, says public service managers must be prepared to indulge in risk-taking behaviour.

"The biggest challenge within the APS is to build an appetite for the cultural shift," she said

"It's about the appetite for risk, and in the short time I've been here the APS is not strong in its appetite for risk and taking it and understanding that there is going to be failure.

"If you're going to embark on shared services, you have to understand there is going to be failure.

"It's being clear, fail fast and then build again to succeed - that's the culture that needs to shift."

Ms Wilson also told the gathered public servants that bigger was best, and that shared services would not succeed without providers being large enough to save real money by achieving economies of scale, bad news for some of the smaller outfits emerging in the public service.

"Within the current environment, many entities are exploring or offering a shared-services offering," she said.

"This fragmentation, unchecked, is going to decrease the ability to generate scale."