A protest rally against the government's austerity measures is expected to be attended by tens of thousands of trade unionists, anti-war activists and other campaigners on Saturday.
More than 250 coaches have been booked to bring people to the capital, while similar protests will also be held in Belfast and Glasgow.
The event is aimed at calling on the coalition to end its public sector spending cuts and other austerity measures.
Civil servant Richard Evans, firefighter Cerith Griffiths and teacher Steffan Ap Dafydd have spent the past week walking 150 miles from Cardiff to highlight the protest.
Evans said: "The cuts being made under so-called austerity measures are vicious and hit the most vulnerable in our society hardest, while those who can afford to pay more get tax breaks."
Griffiths said: "We now see 1,500 fewer firefighters, 130 fewer control staff and some 700 fewer support staff since the coalition came into government.
"The Fire Brigades Union and fire chiefs are warning that a further 2,500 firefighter posts could be lost along with the closure of some 31 fire stations. This puts everyone at risk. More people will die in fires, in floods, in road traffic collisions."
Welsh teacher Steffan Ap Dafydd said: "One hundred and eighty years ago, only one in five men, and no women, had the vote. The rich kept workers down and bent the law to keep trade unions out.
"The descendants of those rich boys do not care about you and me. They still cut tax for themselves and cut pay and benefits for teachers, other working people, the poor, the disabled and pensioners."
TUC general secretary Brendan Barber said: "The evidence is mounting that austerity is failing. More than 2.5 million people are out of work, a further three million are not working enough hours to make ends meet and wages have been falling every month for the last three years.
"Saturday is a great opportunity for people across England and Wales to add their voice to the growing chorus of people who want an end to austerity and a fairer, stronger economic alternative.
"We are working closely with the police and other authorities to make a safe, well-stewarded and family-friendly march.
"People from all walks of life - from unemployed youngsters to seasoned campaigners - will be marching together for a future that works. I hope you will join me on the march on Saturday."