Peace pilgrims were due to arrive at Downing Street on Friday after a two-month trek from Iona to hand in a petition against the Trident nuclear missile programme.
The 2013 UK Justice and Peace Pilgrimage took campaigners some 750-miles from the tiny Scottish island past the Faslane naval base and Edinburgh, to Westminster.
The petition, supported by the Church of Scotland, asks the Government to stop plans to renew Trident and spend the money on education, the NHS and social welfare.
The pilgrimage was inspired by last year's Olympic torch relay and was intended as a Christian witness to the calling to be peacemakers.
Their arrival in London has coincided with a heated Cabinet debate over the missile system's future after the Lib Dems demanded a downgrade.
The Very Reverend Dr Alan D McDonald, former Moderator of the General Assembly of the Church of Scotland, joined campaigners for part of the pilgrimage.
He said: "It seemed like an impossible dream when this little group of pilgrims left Iona on Pentecost Sunday, 19 May. It has been utterly inspiring to see the effect this peaceful walking can have in the unlikeliest places.
"I have joined the walk for the last three days and will be at the finish in Trafalgar Square on Saturday. How hopeful it is, that as the pilgrims arrive in the heart of London, suddenly everyone in the country seems to be talking about Trident. Who knows where this pilgrimage will lead next."
The pilgrims are opposed to Government plans to spend up to £100bn renewing the Trident nuclear missile system at a time when stinging cuts are being made to budgets for health, education and social welfare.
Jill Saunderson, who has walked the full 750 miles, said: "From the day we left Iona, in all the communities we've walked through, the reception has been absolutely incredible. What is most exciting is that we will never know the debates about Trident that have started in these places once we've passed through. In the 9 weeks, not one of the walkers has been ill, other than a few blisters."
Rev Sally Foster-Fulton, Convener of the Church of Scotland's Church and Society Council said: "We are financially and morally better off without nuclear weapons. The money spent on nuclear weapons could be better spent elsewhere, especially when so many people in our society are going hungry.
"Our friends walking the 2013 UK Pilgrimage for Peace from Iona, via Faslane and Edinburgh, are in London. I applaud their efforts and just wish I could have been a part of it."
A paper published this week at the request of the Lib Dems suggested Britain could reduce the current Trident fleet of four submarines.
The United Reformed Church, Methodist Church and Baptist Union of Great Britain welcomed the review's findings, saying the money currently spent on Trident would be better spent on public services and generating more employment opportunities.
Roberta Rominger, General Secretary of the United Reformed Church, said: "Trident is a hangover from the Cold War era. Priorities today have changed."