There needs to be a "genuine and meaningful" public debate on whether the UK should keep its nuclear weapons, the Commons defence committee has said.
Trident was developed during the final decade of the Cold War
Its MPs said the arsenal "could serve no useful or practical purpose" in defeating international terrorism.
This is "the most pressing threat currently facing the UK", they said.
They added the Ministry of Defence must justify the retention of weapons after hearing no evidence of an impending military threat from other countries.
"If the MoD believes in the value of the nuclear deterrent as an insurance policy, rather than in response to any specific threat, we believe it is important to say clearly that is the reason for needing the deterrent," the committee said.
The government should also clarify whether it believed the nuclear deterrent was important to Britain's "international influence and status", the committee said.
"We accept that future threats are unknowable, but, clearly, a world in which nuclear proliferation had taken hold would create deep uncertainties in international relations."
Former environment secretary Michael Meacher also added his voice to calls for a debate, adding there might even be a case for a referendum on the issue.
He said the country had been "bounced" into replacing Britain's nuclear weapons by Chancellor Gordon Brown.
The MPs' call comes as ministers ponder whether and how to replace the Trident nuclear weapon system.
Mr Brown signalled his personal support for maintaining Britain as a nuclear power in a speech this week.
Downing Street has promised a parliamentary White Paper on the issue but has refused to commit to holding a vote in the Commons.
A spokesman for the Ministry of Defence said the department would respond to the MPs' report in due course adding that much of the work suggested by the committee was already underway.
Labour Party chair Hazel Blears pledged "a full debate", saying it was an important issue for the long-term future of the country.
"It's right that we have that discussion, but we have got a manifesto commitment and I think the public expect political parties to keep to their manifesto commitments."
Julian Lewis, Conservative defence spokesman, criticised the MoD's refusal to co-operate with the committee's inquiry, saying: "Despite the prime minister's promise of a full and open debate on the independent nuclear deterrent, it is clear that the opposite is the case."
He said it was "vital" to have "full parliamentary scrutiny" on "a matter of such national importance".
The MoD insisted that it had co-operated by providing written submissions.
Liberal Democrat defence spokesman Nick Harvey backed the committee's call for a public debate.
Decision 'this year'
He said: "Blair and Brown's rival macho posturing is stifling the national debate on Trident's replacement.
"The questions raised by this report must be answered before any decision is made."
Britain has four nuclear-powered submarines, each of which can carry up to 16 Trident II D5 missiles.
Every missile can hold 12 nuclear warheads and one of the submarines is always at sea at any time.
The MoD says this is important so that a potential enemy could not misinterpret the appearance of a British nuclear vessel as a deliberate escalation of force.
The four Trident missile submarines are expected to end their operational life sometime in the mid 2020s.
And the 48 warheads have a similar operational timeframe.
A replacement system would need many years of development and Tony Blair has said a decision regarding the issue will be taken "this year".
A poll for BBC Two's Daily Politics suggested the majority of people were in favour of replacing Trident, with 65% saying provided other countries had them, the UK should have its own nuclear weapons whatever the cost.