Politics - I keep telling my students - is a nasty business, in which principle counts for little and pragmatism - cynical and often heartless - counts for a great deal.
The late Michael Foot, for instance, was a man of principle, and therefore a very unsuccessful politician. Tony Blair, by contrast, was a survivor, a Thatcherite leader of an ostensibly socialist party. Behind him, waiting in the wings, was of course Gordon Brown, a professional student of politics as well as a consummate practitioner.
In a few weeks' time, Mr Brown will ask us to bestow our trust in him and his government by supporting them at the polls. Can he be trusted to keep his word? Can his ministers be trusted to keep theirs?
On the evidence of the story of Labour's betrayal of its undertaking to amend the law of "universal jurisdiction", the answer must, I am afraid, be a resounding No.
The incontrovertible facts were set out succinctly by Martin Bright in last week's JC. Three months ago, the Prime Minister and his Foreign Secretary, David Miliband, announced, in the wake of the threatened arrest of Tzipi Livni should she set foot on British soil, that the law would be changed so as to eradicate the possibility of foreign dignitaries finding themselves at the receiving end of politically motivated British arrest warrants.
From this undertaking there has been an undignified but resolute retreat, the blame for which Martin Bright lays at the feet of justice secretary Jack Straw.
I have no reason to doubt this, recalling as I do the part played by Mr Straw in the downfall of Tony Blair in the summer of 2006. We know (as I wrote on this page on September 29 of that year) that the Cabinet revolt that led to Mr Blair's fall from office was triggered by a statement made by Mr Straw at the end of July 2006.
"Mr Straw", I wrote, "had met leaders of the considerable Muslim community in his Blackburn constituency. Following that meeting, Mr Straw issued a public statement in which he launched a blistering attack on Israel's bombing strategy in Lebanon." But what really angered Jack Straw was Tony Blair's refusal, in Cabinet, to identify himself with the left's hatred of the Jewish state and, specifically, to condemn in public Israel's military strategy in the Hizbollah war. Blair, to his credit, refused to do any such thing. Thus, his fate was sealed.
At the time, I received a number of protests from JC readers reluctant to accept the Alderman version of Tony Blair's downfall. But the following March, in a BBC2 documentary, it was Jack Straw himself who revealed that Blair's support for Israel had indeed "triggered" (his word) the party rebellion that brought about this downfall. Now, three or so years later, it would appear that Mr Straw has again played the anti-Israel card.
The "consultation" exercise that, as justice secretary, he has now ordered means that the universal jurisdiction law will not be amended before the general election. That, of course, is precisely why Mr Straw has ordered it. Once the election is over, who knows? If there is a hung parliament, Gordon Brown may still be in office, but not in power. The law will remain unchanged.
But, although I have painted Jack Straw quite properly as the villain of the piece, Gordon Brown does not deserve to be let off the hook. After all, it is he who is Prime Minister. And it was he who, in the Daily Telegraph of March 3, condemned those political mischief-makers who exploit universal jurisdiction for the purposes of gesture politics. True, he also said in that article that there would be consultation. But hadn't he said that it was his "full intention to legislate as soon as possible".
Well, it is possible to legislate now. If Prime Minister Brown is a man of principle, he will brush aside the protests of his backbenchers, and push the legislation through (there is just enough time), with the support of other parties if necessary. That is what a statesman would do. A mere politician, on the other hand, would take care to wriggle out completely from any rash promise, and would demand a pat on the back for having done so.
As what, Gordon Brown, do you wish to be remembered? Principled statesman? Or grubby politician?