By Paul Reynolds
World Affairs correspondent, BBC news website
With Iran defying the Security Council over its enrichment of uranium and the United States threatening further pressure, there are signs of organised grassroots opposition emerging to any military attack.
Iranian President Ahmadinejad defies the UN Security Council
A pressure group in Britain has urged a diplomatic solution. There are stirrings among religious leaders and members of parliament.
And three senior retired US military officers have said that they "strongly caution against the use of military force". They have called on Britain to play a "vital role in securing a renewed diplomatic push".
'Counter-productive and dangerous'
The pressure group, called Crisis Action, brings together trade unions, charities and Christian and Muslim organisations. They include the Amicus, Unison and GMB unions, the Oxford Research Group, the Foreign Policy Centre, Pax Christi, the Muslim Council of Britain and the Muslim Parliament. The group's document is entitled " Time to Talk".
It says: "The consequences of any possible future military action could be wholly counter-productive as well as highly dangerous. Diplomatic solutions to the Iranian nuclear issue must be pursued resolutely."
One of its spokesmen is Sir Richard Dalton, who was British ambassador in Iran until March 2006, though he is not a signatory to the document and differs on one significant aspect.
But he agrees that the military approach is not the way forward.
"There is no legal basis for an attack," he said. "The negotiating road is hard but could be improved if Iran was offered a regional security assurance and the United States became more directly involved to reduce the issues between themselves and Iran."
However he did not agree with the suggestion in the Crisis Action document that the Security Council demand for a suspension of enrichment by Iran as a pre-condition for talks is a "fundamental" obstacle.
"Suspension is an essential first step," said Sir Richard.
Iran has been offered a co-operation package to develop its civilian nuclear programme as well as the participation of the US in those talks, but first it has to suspend enrichment and the thrust of the offer is that this suspension should become permanent until such time that Iran can gain the trust of the international community.
Generals close ranks
The call by Crisis Action has been backed up by a letter to the Sunday Times from three former senior US military commanders - Generals Robert G Gard Jr and Joseph P Hoar and Vice Admiral Jack Shanahan. General Hoar is a former commander in chief of US Central Command, which covers the Middle East.
Their statement says: "An attack on Iran would have disastrous consequences for security in the region, collation forces in Iraq and would further exacerbate regional and global tensions. The current crisis must be resolved through diplomacy.
"There is time available to talk."
How much time?
The time available depends on how long Iran will take to master the technology of enrichment.
The latest report from the International Institute for Strategic Studies in London (IISS) refers to Iran's expected declaration this week that it will install 3,000 centrifuges in addition to the 164 they have already announced.
"If and when Iran does have 3,000 centrifuges operating smoothly, the IISS estimates it would take an additional 9-11 months to produce 25 kg of highly enriched uranium, enough for one implosion-type weapon. That day is still 2-3 years away at the earliest."
Norman Dombey, Professor Emeritus of Theoretical Physics at Sussex University thinks it could be even longer.
"It would probably take about two years to install and run [the 3,000 centrifuges] and another two before they could enrich enough uranium for one weapon," he wrote in the Independent on Sunday.
Enrichment to weapons grade, as opposed to nuclear power grade, presupposes that at some stage Iran either defies or departs from the Nuclear Non-Proliferation Treaty, under which it has undertaken not to produce a nuclear bomb - and it says it will not do that.
In response to the 'Time to Talk' document, Lorna Fitzsimons, Chief Executive of the British-Israel group BICOM, said:
"The only way economic and diplomatic sanctions will work is if Iran realises that the credibility of a military strike is real. Iran thinks the US is weak and that Iran is in the ascendancy in the Middle East. That is why Iran's leaders do not feel the pressure or the need to work with the IAEA. The only way to make soft power a success in Iran is to ensure they realise that the hard power of military actions is a last resort reality."