Any action which the UN security council takes against Iran over the nuclear dispute must be "incremental and reversible", the foreign secretary, Jack Straw, said today.
Speaking as the security council began to discuss its response to the long-running row, Mr Straw said the west was "right to be worried" about Iran getting an atomic bomb.
He said the UN should seek a "full verifiable suspension" of nuclear enrichment and reprocessing research in Iran, while at the same time keeping the door to negotiations open.
The UN's nuclear watchdog, the International Atomic Energy Agency, referred Iran to the security council last Wednesday after efforts to break the impasse failed.
Mr Straw said comments from Iranian leaders were increasingly provocative. However, he added: "Security council involvement does not mean an end to our efforts to find a negotiated solution. It marks a new phase in diplomatic efforts."
In a wide-ranging speech on Iran at the International Institute for Strategic Studies in London, he said that Iranians "deserved better" than a regime which was taking the country "in the wrong direction".
The region would be seriously destabilised if Iran gained atomic weapons and other states would be encouraged to get nuclear bombs, he said.
Iran should be supported in getting civilian-use nuclear power but it should not be allowed to do its own enrichment work, Mr Straw said.
Addressing Iran's complaint that there was no consistency in western diplomacy because Israel had nuclear weapons, he said the UK wanted Israel to join the non-proliferation treaty.
The UK had also signed a proposal in 1995 calling for the whole of the Middle East to be nuclear-weapon free. Iran getting the bomb would be a "serious" obstacle towards this goal, he said.
Mr Straw also noted that Israel had not recently called for Iran to be "annihilated", in contrast to the call by the Iranian president, Mahmoud Ahmadinejad, for Israel to be "wiped off the map".
Tehran denies US and western claims that it plans to develop a nuclear weapon and has refused to resume suspension of its experimental enrichment activities.
But Mr Straw cast doubt on these claims. He said Russia had offered to help Iran run for the next 10 years the one nuclear power plant it is building, and would do so indefinitely if asked. He said it was unusual for a country with one nuclear power station to want to do its own nuclear enrichment work.
He added that military personnel were involved in Iran's nuclear programme and the regime had a record of misleading the international community on its true intentions.
He said it was not just Europe and the US who had concerns about Tehran's nuclear ambitions and there were anxieties around the world.
Iran had a young, educated population but prolonged dispute with the international community would damage the country's economy, the foreign secretary said. Many bright young Iranians were already "voting with their feet" and leaving the country.
"Our message is that we want the Iranian people to enjoy the benefits of civil nuclear power and we support their aspirations for a freer, more democratic and prosperous Iran."
Iran was not making the most of changes in the region, he said. "The chances that Iran has to capitalise on the fact that they no longer have a belligerent dictator on their doorstep in Iraq nor an aggressive Taliban in Afghanistan are being squandered."
He said Iranians must wonder why Shia Muslims in Iraq could vote for who they wanted, while Iran's parliamentary elections in 2004 and last year's presidential elections were restricted.
Freedom of the press had been seriously curtailed and Mr Straw called on international media groups to help inform Iranians, for example, by publishing news online in Persian.
His comments follow a move by the US secretary of state, Condoleezza Rice, to request funds from Congress for a huge cultural outreach programme targeting Iranians.
Mr Straw said: "We will not take sides in Iran's internal political debates, those are for the Iranians to resolve. But this does not mean that we should stop standing up for the principles of human rights and fundamental freedoms which we hold dear to ourselves and which so many Iranians aspire to."
Earlier, Mr Straw said Tehran had repeatedly miscalculated by thinking it could split the UN and renewed his insistence that military action against Iran was inconceivable.
He told the BBC Radio 4 Today programme: "This is not Iraq for a moment.... This is an issue that has to be resolved, yes by pressure, but by peaceful and by democratic means. Although no American president is ever going to theoretically rule out any option, in practice military action is not on the Americans' agenda."
He said Mr Ahmadinejad was a "difficult individual to deal with" but ultimate decisions rested with the country's ruling theocracy.
The Liberal Democrat foreign affairs spokesman, Michael Moore, said: "The foreign secretary's direct appeal to the Iranian people recognises the complexity of Iranian politics and the range of opinions within the country. That recognition needs to be shared by the US so that the UN's diplomatic process does not inevitably slide down a route towards conflict."
