Many more will join marches in Glasgow and Belfast on the same day to tell the government its austerity policies are not working and to call for an alternative economic strategy that puts jobs, growth and people first.
In London tens of thousands of people are expected to march the nearly three-mile route from Embankment to Hyde Park, looked after by hundreds of stewards.
Marchers will begin to assemble on the Victoria Embankment on the north bank of the Thames from 11am, between the Hungerford Bridge and Blackfriars Bridge.
The march will set off at 12 noon, with departure times staggered depending on where in the line-up members are. Prospect members are assembling at Section 10 of the line-up, which will be signposted.
Those coming by public transport are advised to join the march from the rear, arriving at stations like Blackfriars and St Pauls (on the north side of the river) or Southwark (on the south side).
The march will finish at Hyde Park, where a rally with speakers, music and films will take place from 1.30pm-4pm. Over 250 coaches are booked to come down to the capital – for details see the False Economy website
The TUC has issued some top tips for first-time marchers on its website.
Protestors have also been speaking on the TUC's Stronger Unions blog, including Prospect member Ele Wade, a rep at the Intellectual Property Office in Newport, South Wales.
She says: "I will be marching because I believe the coalition's austerity policies are counterproductive, reducing support for innovation and taking money out of the economy."
Prospect general secretary Paul Noon said he would be marching because: "Austerity isn't working and we need a plan for growth. Members from all over the country have been telling me they will be there on the day to send a loud and clear message to government that it needs to change direction."
Best banners and placards
The TUC, along with Guy Atkins of Goldsmiths University, has also launched a best banner or placard competition. The Make our March contest will be judged by artists Bob and Roberta Smith, comedian Josie Long and the Mirror's Kevin Maguire.
It is offering five £100 prizes for the most creative or funniest contribution to the march. People can upload their contribution to the Make the March website in advance to have a chance of winning. It's not just placards, there will also be a prize for the best graphic or video uploaded.