New readers start here: Damian Green, a Conservative opposition spokesperson on immigration had his parliamentary and other offices raided by police investigating the leaking of secret information from the Home Office. The Director of Public Prosecutions (DPP) has decided there is insufficient evidence to proceed with a prosecution against Mr Green and his leaker, civil servant Chris Galley.

The DPP ruling has tightened the definition of what constitutes criminal offence when it comes to leaking. But the protestations of Mr Green, and the Conservative party, that he was just “doing his job” as an opposition politician are more than a little problematic.

Let’s think about this for a moment. Mr Green systematically met with and encouraged – some have indeed called it “grooming” – a supposedly neutral civil servant employed in the private office of the Home Secretary to leak politically useful information to him. Is this really “just doing the job” of opposition?

If Mr Green’s tactics were duplicated across the whole of government then civil servants in every private office of every minister in Whitehall would be encouraged to leak to opposition politicians. Or be potentially suspect for doing so. What would be the consequence?

Ministers would be forced to conclude the civil service was untrustworthy and we would rapidly go down the route of having only political appointees in senior positions. Is this really what the Conservatives want? A politicised senior civil service? It is usually governments who are accused of politicising the civil service – but oppositions can make their contribution too. There may be merits in such a policy – many western democracies have such a system – but it merits more of discussion before we go down such a route. The immediate political advantages of leaks are surely not a sufficient grounds for such a change in policy?

Let’s ask: would a future Conservative government really be comfortable with the idea that civil servants could selectively leak from minister’s private offices depending on their political inclinations? Merely asking the question answers it – of course they would not. If it happened they would be incandescent with fury.

Also, despite the DPPs conclusions, we have to ask: can a systemic leak in one of the most sensitive ministries in government (dealing with internal security) really be considered just a routine matter of legitimate opposition politics? No really security-sensitive information was leaked – but who was to say it would not have been?

The Conservatives are playing fast and lose with serious constitutional issues here – just as they have around recent policing issues (to which this is linked). They – and we all – may well live to regret their opportunism.