First Minister Peter Robinson was furious last week over the stories that appeared in the national press about the political income he and his wife Iris obtain.

Although, as he said, his only crime is being married to another MP and therefore getting two huge incomes for the family, he regarded the story as one manufactured by political opponents.

He pointed an accusing finger at the Ulster Unionist party, which he said had fed the details of his income into the Conservative Party’s “sleaze machine”.

Although Ulster Unionists have denied the claim in the strongest possible way, it is understandable why Mr Robinson came to that conclusion. The unionists have joined forces with the Tories to fight future elections and the Robinsons are two obvious targets.

What Mr Robinson was suggesting was that political opponents will stoop to any level for political advantage. There are many people in Northern Ireland who are envious of the Robinsons’ earning power and pandering to that envy may win opponents some votes.

But Peter and Iris must be glad they were not targets of the Labour Party’s dirty tricks machine if the stories which emerged at the weekend prove true.

Damian McBride, Downing Street’s head of strategy and planning, has been forced to resign after an alleged smear campaign orchestrated by him and directed at senior Tories was uncovered.

The campaign allegedly planned, by insinuation and downright lies, to suggest that Conservative Party leader David Cameron had once suffered a sexually transmitted disease and that Shadow Chancellor George Osborne once cavorted — or worse — with a prostitute and that damaging pictures of his private life exist.

Most offensive of all were suggestions about the mental health of Mr Osborne’s wife, Frances.

Some of these stories were apparently described as “absolutely totally brilliant” by colleagues of Mr McBride. What world do these spin-doctors live in?

We all know that politics is a dirty business and that some very unsavoury people inhabit that world. Of course, political parties — or at least those with any realistic chance of gaining power — will do everything possible to smear their opponents.

However, we usually expect the smear to be based on policy issues — for example Labour’s handling of the economic crisis — or, failing that, on the truth.

Yet, it appears from the weekend reports, that malicious gossip and political tittle tattle is a strong enough foundation on which to build a tissue of lies and half truths. Never mind that such misinformation could destroy a person’s life or relationships. All that matters is political success.

Even Alastair Campbell, one of the most bruising spin-doctors of recent times, described the alleged stories as unpleasant, as well as incompetent — presumably because they were discovered.

These stories and the planned campaign behind them were of a completely different order to the stories which circulated about the Robinsons’ earnings. Everyone knew that Peter and Iris are coining it, and this newspaper has run several stories with the details, all gleaned through perfectly reputable and defensible methods.

All that makes the Robinsons different from other Northern Ireland MPs is that there are two of them living in the same house, or houses. Individually, they are not even the highest claimants of expenses.

But imagine if some political opponents began spreading rumours about their married life or about the relationships of other senior DUP politicians, especially if those stories were not true.

The problem is that when such stories become public, the ordinary internet browser or newspaper reader or television viewer has no way of knowing if the stories are based on fact or not. The internet, for example, is stuffed full of blogs which have no basis on reality, but which can damage their targets.

The Prime Minister should put down a marker for decency and state without equivocation that manufactured sleaze stories have no place within the Labour Party and he should apologise to the intended targets.