The Liberal Democrats have said they will not replace Trident nuclear-armed submarines, but they have still not broken the overall nuclear hold on their defence policy, say critics - including environmentalists and disarmament campaigners.
The challenge was echoed by the leader of the Green Party in England and Wales, Caroline Lucas, in a speech late last week at the Flame of Hope rally was held as US President Obama and Russian President Medvedev signed a new nuclear arms reduction treaty, cutting the number of warheads held by Russia and the US.
The rally marked the Brighton to Worthing leg of the South Coast Relay, an initiative by Abolition 2000, a global network to abolish nuclear weapons. It is raising awareness of the crucial Review Conference of the Nuclear Non-Proliferation Treaty in May 2010.
Ms Lucas, who is hotly tipped to become Britain's first Green MP in Brighton, declared: "The Lib Dems tell us that they want to scrap Trident. What they don't tell you is that they would still keep a nuclear deterrent. The Greens are the only party who believe that a nuclear-free world is both necessary and possible."
She added: "Disarmament isn't a dream. It can happen, and has happened in many places around the world. In a few short weeks, the British electorate has the opportunity to have its say too. We must send a message to all parties, that replacing Trident is immoral, irrelevant - and a cost simply not worth paying."
The Green Party figurehead explained: "Initial estimates suggested that the cost of Trident replacement would be in the region of £25 billion. That's the equivalent of the money needed to pay for 60,000 newly qualified nurses and 60,000 new secondary school teachers for the next 10 years.
"Recent estimates suggest that when the annual costs of maintaining a replacement for Trident throughout its life are added in, we're looking at a bill of nearer £76 billion. To use that amount of money on a project that will make Britain and the world a far more dangerous place is politically irresponsible, morally bankrupt, and economically obscene."
Ms Lucas concluded: "The £76 billion price tag for Trident replacement is desperately needed elsewhere, for energy efficiency, energy conservation, and renewable energy, making us more secure by reducing the impacts of climate change, and by ending our dependence on foreign oil - a key root cause of global terrorism."
The Labour government is committed to Trident replacement, in spite of the astronomic costs, and in spite of questions from military analysts about the values of the system - as well as strong moral objections from peace groups and churches.
The Conservatives have also been enthusiastic Trident backers, and helped the government push the replacement policy through parliament.