There was once an old political saying – variously attributed to both Stanley Baldwin and Harold Macmillan – that neatly defined the limits of state power in the middle part of the 20th century.
"There are three bodies no sensible man directly challenges: the Roman Catholic Church, the Brigade of Guards, and the National Union of Mineworkers," it went.
Times change, of course, and a modern rendition would undoubtedly have different bogeymen in the guise of those with whom no government dare fall out.
Media baron Rupert Murdoch, as we saw in last week's column, would certainly be one. The all-powerful motoring lobby might be another. But if you had to pick a third, it would probably be the Police Federation.
Attempts to reform the police over recent decades have invariably foundered as soon as the Federation – as influential a trade union as the NUM once was – started flexing its muscles.
Three years ago, the then Labour Home Secretary Jacqui Smith tried to shelve a police pay increase that had been awarded by an independent assessor – and was swiftly forced to back down.
Fifteen years earlier, Ken Clarke – no softie he – had launched a much more wholesale attempt at reform.
When Clarke moved from the Home Office to the Treasury it landed in his successor Michael Howard's inbox - but even that legendary political hardman decided a scrap with the boys in blue was not worth the candle.
So it is not without political significance that this week has seen the publication of a brace of reports which taken together amount to something of a double whammy for police pay and conditions.
On Tuesday, former rail regulator Tom Winsor published the results of a review calling for the abolition of overtime payments worth up to £4,000 a year to officers.
The following day, Lord Hutton – that's former Barrow MP John Hutton rather than Tony Blair's favourite retired judge – published a much more wide-ranging review into public sector pensions.
Among other things, it recommended not only the end of final salary pension schemes in the public sector, but an increase in the retirement age which would see police, members of the armed forces and firemen working till they were 60.
Already, the public sector unions – including the Federation - have made clear that the government has a big fight on its hands if it tries to implement this week's proposals.
As Unison's Dave Prentice put it: "This will be just one more attack on innocent public sector workers who are being expected to pay the price of the deficit, while the bankers who caused it continue to enjoy bumper pay and bonuses."
There are certain to be demonstrations, possibly even strikes, which will put the Police Federation in an interesting position to say the least.
For of course its members will be expected to control the protests called by those campaigning against the very proposals which they and their colleagues are being threatened with.
In one sense, this is a reform whose time has come. Final salary pension schemes are a thing of the past across most of the private sector, and in that context the retirement benefits enjoyed by public sector staff have started to look more and more anachronistic.
Yet the country's six million public sector workers remain a big and powerful constituency for any government to take on, especially in the aftermath of a recession.
Ultimately it may come down to a rather crude consideration, namely how many votes there are in public sector pension reform.
The answer is: probably not many. But there are a great many more potentially lost ones.