By David Porter
Westminster correspondent, BBC Scotland
You know you're getting old when the policemen start to look younger.
The pay agreement is not being fully applied outside of Scotland
As a politician, you also know you're in trouble when those young-looking policemen, together with their older colleagues, fail to show deference, but instead start to show their teeth and call for your resignation.
Labour cabinet ministers at Westminster have been on the receiving end of both this week.
As a general rule it's wise not to antagonise the very people who can throw you in jail.
And the reason for all this anger, a small but vitally important word - PAY.
As befits an organisation built on command and control, the police attack began at the very top.
The prime minister has been characterised by rank and file policemen as a ''Scrooge'' character, unwilling to give them their pay settlement in full.
For the home secretary it was worse - metaphorically the police got their truncheons out and battered her, formally calling for Jacqui Smith to resign.
It's all been made worse by the fact that the Scottish Government has given the police their wage rise in full, backdated into the bargain.
The dispute is not over the level of the rise, but over when it is brought into effect
A case of not just cross-police tensions, but cross-border ones as well.
So how has this row arisen?
Home Secretary Jacqui Smith has decided NOT to backdate a 2.5% pay rise for police in England, Wales and Northern Ireland.
The police say that because the 2.5% rise has been staggered to start in December, this year it will amount in real terms to 1.9%.
The level of the increase was set by the Police Arbitration Tribunal, which is then normally ratified by the home secretary.
The dispute is not over the level of the rise, but over when it is brought into effect.
Ministers in London see it somewhat differently.
According to the Home Office, constables have seen a 36% wage increase since 1997, which is 10% above inflation.
Gordon Brown faces a cross-border disparity between officers
Prime Minister Gordon Brown decided to stage public sector pay rises when he was chancellor.
He has said staging pay awards was an "essential part" of controlling inflation, keeping interest rates low and creating more jobs.
He also said he would "do nothing" that put economic stability or low interest rates at risk.
Why have Scottish officers had their pay backdated?
The Scottish Government agreed to backdate the 2.5% rise to 1 September, as recommended by the Police Arbitration Tribunal.
At prime minister's questions, Gordon Brown was twice asked about the difference north and south of the border.
Firstly, the Tory MP Michael Fabricant coined a new variation on the West Lothian question.
He wanted to know why police in his Lichfield constituency would be getting a worse pay deal than those in Linlithgow?
Later, the SNP's Angus Robertson decided to ginger things up a bit.
The police are a well organised pressure group and are now planning to hold a ballot on the possibility of strike action
He invited the prime minister to praise Alex Salmond for the police pay deal on offer in Scotland.
Unsurprisingly, Gordon Brown managed to resist this temptation.
Instead, attack was deemed the best form of defence.
He chided Scottish ministers for falling short on their promise to deliver 1,000 new police officers on the beat in Scotland.
But there is real nervousness among many Labour MPs.
They fully support the plans to try and keep a lid on inflation and public sector pay, but some are worried this is a fight they cannot win.
The police are a well organised pressure group and are now planning to hold a ballot on the possibility of strike action.
(In fact they won't strike because that would require a change in the law - but any such vote would send a pretty clear message to ministers).
Granting the pay rise in full would cost the UK Exchequer about an extra £40m - some MPs are now muttering that is a small price to pay to avoid such a damaging row.
Meanwhile, in Scotland, politicians and police officers look on with interest, but not a direct financial one.
No-one expects hordes of law enforcement officers to up sticks and head to Scotland for what at the end of the day is the sake of a couple of hundred pounds.
But this dispute is another interesting example of devolution in practice with different policies in England and Scotland.