The future of the UK's Trident missile deterrent could be affected if Iran develops nuclear weapons, Foreign Office Minister Kim Howells has said.
Mr Howells said any such development would throw the question of nuclear deterrence "back into the boiling pot".
But Iran would not be able to produce nuclear weapons for "some time yet", he added. Trident received a £1bn boost in July to ensure the system is reliable.
Mr Howells was speaking as Tory MPs voiced concern over Iran's regime.
Mr Howells, responding to a question about the future of Trident, said: "If Iran does develop a nuclear weapon, it throws the whole of the issue about how we get rid of our nuclear stocks, how we demilitarise, back into the boiling pot."
The comments came during a Westminster Hall debate suggested by David Amess, Tory MP for Southend West.
Mr Amess said the government's policy of "rapprochement" had allowed radical elements in the current Iranian regime to strengthen their control.
He added that the regime posed "a real and present threat" to its own and the Iraqi people, citing issues including efforts to export fundamentalism, sponsorship of terrorism and the development of nuclear weapons.
Mr Howells said there was "absolutely no explanation" for Iran's programme of nuclear conversion and that there were "very, very worrying things" happening in Iran at the moment.
Tory MPs called for an end to the policy of engagement with Iran and said the government should refer it to the UN Security Council over its nuclear activities.
However, Kate Hudson, chair of CND, said it was "outrageous" to use Iran as an excuse for proliferation of nuclear arms.
"The concern is that this danger of proliferation can be used in a political way. We saw it in Iraq, where the government believed there were weapons," she said.
"Many people are concerned that something similar is happening with Iran.
"The best way to deal with this is to have all countries comply with the NPT [the Nuclear Non-Proliferation Treaty] and begin disarmament."
The debate came after Iran denied being involved in explosions in Iraq which killed eight British soldiers in the last five months.
But Prime Minister Tony Blair has warned the regime that it had been linked to recent attacks.
Mr Amess expressed concern over Iranian president Mahmud Ahmadi-Nejad, who he said had been accused of being a murderer and a terrorist, as well as plotting to kill author Salman Rushdie.
He said the Iranian cabinet was a "who's who of terrorism" and that the rise of Mr Ahmadi-Nejad revealed moderates in the government had been eclipsed.