What to make of the departure of Sir David Varney from HM Revenue & Customs?

He has got a new job which many are describing as at least a sideways step - as an adviser to Gordon Brown on 'transformational government.' Now I don't know whether Whitehall people regard that as a terribly exciting new brief, but it sounds like a lot of hot air to me.

Getting closer to Gordon Brown might be an astute politicial move. Then again, it might be catastrophic if it all goes wrong for Gordon.

The question that keeps nagging is: why not just stay at HMRC? Not only does it present some of the most interesting moral challenges in government, you are also in charge of one of the nation's most powerful law enforcement agencies in Customs, and are responsible for one of, if not the most complex and difficult IT challenge in government.

Why go off and be an airy adviser to the Chancellor? I just can't fathom why you would do that.

There is a cynical explanation. Sir David was having real trouble with the job. His relationship with select committees was always tempestuous - he never got on with the MPs and seemed to lack the charm required to draw the sting.

Carousel fraud was marching ahead, primarily as a result of a misfiring strategy that he inherited, it has to be said. Tax credits had done him enormous damage, and he appeared to add little to the department, having lost control of the policy space to more junior colleagues.

Of all those things, I'd say his discomfort with MPs and his junior colleagues were most important - there are, after all, always negative stories about the tax collecting departments of the tax credits/carousel fraud kind.

As someone who was the pin-up for private sector talent in Whitehall, getting rid of him was a major headache for Gordon Brown. It would have been admitting defeat. So he has ended up with a non-job to make it look like he has been a success.

I don't think, as a matter of fact, that he has been a failure. The merger was carried off with no major hitches, an impressive achievement. He was always pretty much on top of his brief whatever the problems, and is clearly a highly intelligent individual.

But I can't help thinking there's more to his departure than meets the eye.

One thing that might be worth noting is that HMRC is now like no other department in Whitehall. Its minister, Dawn Primarolo, has outlived two permanent secretaries. Are there any other departments, I wonder, that can claim the same feat?