Jon Thompson is to become the new Dame Mary Keegan, taking over the government's overall financial management.

Thompson moves into the position next month with a sterling reputation as director general of corporate services at the Department for Children, Schools and Families.

But it is his plan to continue in this role while taking on the position as head of government accounting that has become a bone of contention for politicians.

What's happened?

MPs have blasted the appointment as Thompson will juggle his new role and his current role as director general for corporate services at the Department for Children, Schools and Families.

They've scorned his 'part-time' role at a time when government accounting has taken a public battering for not being ready to switch to international financial reporting standards, as well as being elusive as to how it will deal with masses of controversial PFI debt - sure to break the government's own sustainable investment rule.

Despite the scathing 'part-timer' label - odd for a man who works a 70-hour week in his current role - there isn't any malicious hint of incompetence on the part of Thompson.

At the news of his appointment, the Treasury's permanent secretary Nick Macpherson commended Thompson for transforming financial management in his department, and said Whitehall would benefit from his wealth of private and public sector experience and expertise.

But MPs appear to have little faith that Thompson will be able to whip the whole of Whitehall into the leaner and more efficient operation that it should be, if he's going to be dividing his time and energy to that of the equally demanding Department for Children, Schools and Families.

What's going to happen?

For now, the Treasury seems to be sticking to the plan to allow Thompson to wear two hats.

He has his work cut out for him but he's recently built more capacity into his current department - which may allow him the leeway to focus more on Whitehall's accounting problems at large.

But it still isn't clear how Thompson will manage the dual roles.

Some might even question whether there could be issues over conflict of interest.

Thompson is said to have a remarkable skill for seeing numbers as colours and having a quick grasp of spreadsheets as a result.

Whatever else happens, remarkable is what he will need to be in his new roles.