The key word is “irreversibly”. India had not wanted to make this concession, for fear it would put a cap on military work. But many would say that it makes little difference.

India is still free to expand its military programme. It probably has enough plutonium already for all conceivable needs. And, some sceptics say, “irreversible” is a slippery word in diplomacy, as the years go by.

The deal does offend the principles of the NPT. Under that treaty, apart from the five states that were first to get nuclear weapons (US, Russia, China, France and Britain), countries were to receive help with civil nuclear power only if they did not seek weapons.

India, which has never signed the NPT, shocked the world with its nuclear test in 1998. Pakistan promptly followed suit.

Critics say that this agreement sends unhelpful signals to Iran.

On Monday, the board of the IAEA will meet yet again to discuss how to put pressure on Iran to discourage it from its nuclear ambitions (which it insists are entirely peaceful).

For that reason alone, Congress will give Bush a hard time as it considers the terms. So will the Nuclear Suppliers Group, the 45 countries that trade in nuclear technology. The group includes China, which may threaten to withhold support unless the US says a similar deal for Pakistan could be in the offing.

But is the deal really that damaging? For years, those battling to enforce the NPT have had to grapple with one glaring fact: India, Pakistan and Israel all have nuclear weapons (assumed if not declared, in Israel’s case). Yet none of them has signed the treaty.

Mark Fitzpatrick, non-proliferation specialist at the International Institute for Strategic Studies in London, says that the “positive” part of the deal is that “it recognises that India cannot be treated as a pariah for ever” because it has the bomb.

How should the credibility of the NPT be upheld, in trying to lean on Iran? He argues that it can be, by spelling out why India is not like Iran: “It has a record of keeping its commitments, protecting its (nuclear) technology (and not exporting it), and it is an open and pluralistic society.”

This is surely right. The importance of Bush’s trip is that it acknowledged — much too late, in many ways — that India’s importance cannot be overlooked.

Critics will call him opportunistic for giving this giant help that he wants the world to deny Iran.

But this is one time when realism is justified. Yesterday’s imperfect deal is good news.

Backing off drug farmers

Not much about the Afghan drug war is good news.

“In the past, we’ve not targeted the people we should have done,” said Kim Howells, the Foreign Minister, yesterday.

“There’s no point knocking down the crops of ordinary farmers — we’ve got to go after the wheelers and dealers.”

Yet he also says that British forces, soon to be sent to the heart of the drug region, will focus on getting intelligence.

“It’s not our job to go in there and take them out,” he said.

Britain, which is the lead nation on counter-narcotics in Afghanistan, will spend £270 million in the next three years. But it will not pay farmers to give up poppies, a controversial tactic about which Howells says he has “mixed feelings”.