Steve Coogan has become the latest high-profile figure to call on the government to provide more school funding.
The actor and comedian, whose daughter attended a Brighton state school, is set to deliver more than 30,000 messages, written by pupils, to Downing Street on Thursday as part of a protest against school funding cuts.
The messages have been written by children from more than 60 schools in Brighton, Birmingham, Manchester, West Sussex and the Isle of Wight.
The BAFTA award-winning actor will also make a speech alongside activists from the parent-led Save Our Schools campaign, which is demanding more cash for schools. MPs from the three cities are also due to attend.
The campaigners are then planning to lead a "peaceful action" outside the Downing Street gates, involving a pop-up art installation of more than 20,000 SOS messages in bottles, speeches from two Year 5 Manchester pupils, and a teacher from Birmingham.
After that, the protesters will move to Trafalgar Square, where children will float their messages in a bottle in the fountain. A video of children singing Message in a Bottle and protesting the school cuts has been released by the campaign group.
In a written statement, Mr Coogan said: “I'm fully supporting all the parents leading the fantastic Save our Schools Campaign, forcing politicians to seriously consider the funding cuts to our state school system.
"We cannot live in a society where we have a state education system that is stripped to the bone and where the arts and sport are the preserve of children whose parents can afford to pay for them."
The messages being presented on Thursday include one from a 14-year old pupil from Birmingham, stating: “I would find school really difficult without my teaching assistant.”
Another, from a Year 6 pupil, Tommy, said: “I love my teaching assistants and how happy and jolly they are and how sometimes they sacrifice their lunch breaks to help us.”
One of the Save Our Schools founders, Alison Ali, said: "We’ll continue to protest until schools get their £3 billion per year back, and until our children get the forward-looking, broad-based education they deserve.
"We hope the prime minister, the chancellor and the secretary of state for education are prepared to actually sit and read these poignant messages from tens of thousands of children around the UK and then act upon them.”
Mr Coogan follows in the footsteps of fellow actor Jason Flemyng, who starred in Lock, Stock and Two Smoking Barrels and in May called on politicians "to fund schools properly" in a video featuring his twin sons.
Before last month's general election, celebrity chef Jamie Oliver attacked the Conservatives' manifesto plans to free up funding for schools by scrapping free lunches for infant school pupils.
The Conservatives have declined to confirm that they will stand by their manifesto pledge to provide schools with an extra £4billion by 2022.
Education secretary Justine Greening is reportedly asking for the government to publicly commit, before the holidays begin, to providing an extra £1.1bn for schools.
The government is also yet to provide final details on the national funding formula for schools, which was originally due to be introduced from 2018.