Have a look at the second link Whitey posted, Trousers.
A lot of public sector workers have 'transferred' to the private sector (e.g. hospital cleaners, cooks, porters) bringing down the average of the private sector whereas once it brought down the average of the public sector.
And there are probably a lot more private sector burger jockeys (as an example) than there are low paid public sector workers.
But that doesn't mean, like for like, that public sector workers are better paid than their private sector counterparts.