Gordon Brown is expected to announce his plans in a speech to the United Nations on Thursday.

In a joint statement, the leaders of the Baptist, United Reformed and Methodist Churches said that reducing the number of Trident submarines by one was a “feeble and ineffective gesture” that would do nothing to support moves towards global nuclear disarmament or ease the pressure on public finances.

They said that Trident “makes little sense” in the face of calls from the Ministry of Defence for greater logistical support for frontline troops, and that building three instead of four Vanguard submarines would not significantly reduce the £20 billion cost of the project.

“With health and education expenditure under great pressure public support for Trident is evaporating fast,” they said.

The Church leaders insisted that a nuclear-free world was “realistic” and called upon the Government to follow up its pledges towards disarmament with action.

“Peace and security in the 21st century necessitate the building of fairer global systems in which the benefits of freedom and development are more equally shared,” they said.

“It is becoming ever clearer that our future security cannot rely on the outmoded concept of nuclear deterrence.

“As Christians, we believe that a world free of nuclear weapons is not only desirable but realistic.

“We welcome the Government’s stated commitment to the cause of global nuclear disarmament but urge the Government to combine words and action.”

Trident supporters fear that dropping one submarine would jeopardise the UK’s sea defence, while trade unionists, religious leaders and anti-nuclear campaigners have been campaigning against any replacement for years, believing it to be unnecessary.

In Scotland, where Trident is based, the Church of Scotland and Roman Catholic Church have been unanimous in their opposition to nuclear weapons, arguing that they are morally and theologically wrong.

The Church of Scotland, however, welcomed the proposed reduction of submarines, calling it a “step in the right direction”.

“We welcome the news that the Prime Minister is thinking of reducing the number of submarines from four to three as a first step on a longer journey to nuclear disarmament,” said the Rev Sandy Horsburgh, vice convener of its Church and Society Council.

“The General Assembly has consistently supported nuclear disarmament and we encourage the Government to go further in that direction.”