Number 10 is well-used to Tony's opposition - indeed invariably welcomes it, on the simple rule-of-thumb that if Benn is against something, it is probably playing well with the punters. So Downing Street shrugs off Benn's charge that Blair and the modernisers are selling Labour's soul, pointing to the left-inspired 1983 manifesto which came to be dubbed "the longest suicide note" in election history.
They are similarly dismissive of Tony Benn (a veteran of old-style Labour socialism) and his colleagues on the left when they oppose military action against Iraq - describing Britain's role as sole "cheerleader for US sabre-rattling" and as "the opposite of what an ethical foreign policy would require."
But deep misgivings about the build-up to seemingly-inevitable military action in the Gulf are not confined to the old Labour left. A hero of the last Gulf War spoke out yesterday against the British/US stance, as 10 Anglican bishops declared their opposition to military action, insisting air strikes against Saddam Hussein would not constitute "a just war".
Former RAF pilot John Nichol, who was shot down over Iraq and held by Saddam's troops in 1991, said the last war had failed to resolve the underlying problem of weapons of mass destruction. He accused politicians of losing touch with the reality of war, asserting that the lack of clear objective in the current crisis was placing the lives of military personnel in unnecessary peril.
Nichol insisted: "You must have an aim to achieve and you must at some point be able to say we have now finished our task, and that happened in 1991. But that can't happen at the moment because there is no key task."
Getting Saddam, getting his chemical weapons, said Nichol, were political soundbites rather than military objectives: "they spell danger for people in the military."
The danger posed to vast numbers of innocent Iraqi citizens was central to the bishops' plea to the government to seek "an international consensus" and not allow a "superpower mentality" to make the running. In an open letter they said the use of military force would be "morally weak", and that the large-scale civilian casualties certain to result would "reinforce the already deep Muslim mistrust of the West".
Blair is certain to prove himself as resistant as Thatcher to what the bishops have to say on matters of war. However, for all his enthusiasm to back his pal the US President, the British Prime Minister must surely know the risk he runs in committing to a military enterprise whose lack of clear and achievable objectives is underlined even by those most eager to urge him on.
Paddy Ashdown will stand squarely behind Blair if it comes to it. But he has pointed to an elaborate and necessary diplomatic prerequisite which has not yet been played-out. And Lord Healey (no loony leftie he) has warned against "unwise" military action which could strengthen Saddam and alienate the West's Arab friends.
Negotiation with Saddam was unlikely to succeed unless backed by the threat of force. But the problem with all the suggestions currently canvassed for a strike was that they seemed likely to strengthen rather than weaken him. "The important thing," said Lord Healey, "is to see if there are sensible uses of force against Saddam's military facilities. If there are we should be prepared to hit them."
That is the point central to the disquiet about the proposed action. We are told the objective is to destroy Saddam's capacity to produce chemical and biological weapons. Yet there appears to be no certainty whatsoever that that can be accomplished. The rolling-objective then seems to translate into a bid to wipe out some of his other military capability. This point was certainly underlined by John Major's intervention on Tuesday, when he suggested the action should target Saddam's Republican Guard.
Pointing to the likelihood that Guard commanders, on hearing this (and they have television in Iraq) would locate themselves and their troops around schools, mosques and hospitals, Nichol said the West could not target them without accepting the inevitable "collateral damage." Collateral damage means "civilians on the ground being killed."
Having been tortured by his henchmen, Nichol made it plain he was no apologist for Saddam but he said: "We supported him 10 years ago, we kept him in power and we are now saying we must bring him to heel. How do you do that?" Even if it could be done, "are we then to bring every dictator we don't like to heel all over the world?" The problem with the language of war was that the West was setting itself up as moral judge and jury for the rest of the world. The problem with the language of politics was that "our politicians are painting themselves into a corner and the danger is they are going to have to bomb their way out of it."
Without a dramatic diplomatic breakthrough it seems they will be doing exactly that sometime in the week after next. And the doubters will be discarded as the nation rallies. While there is no war fever here, Blair (not for nothing once called the "Son of Thatcher") knows a clear majority currently approves his "unconditional backing" for President Clinton. Intriguingly the latest ICM poll shows that support strongest among the young.
Thatcher's children are not in the peace camp.