The actress is one of several celebrities uniting for The World’s Big Sleep Out, which aims to raise £40m to tackle homelessness.
The event will see 50 sleep outs worldwide, including events in London, New York, Edinburgh, Brighton, Newcastle, Cardiff, Dublin, Newport, Belfast, Chicago, Amsterdam, Manchester, Madrid and New Delhi.
Dame Helen will read a story in London while Hollywood star Will Smith will tell a bedtime story in Times Square, New York.
Other big names taking part include mayor of London Sadiq Khan, model Lisa Snowdon, Olympic champion Sir Chris Hoy, singer Jamelia, author Giovanna Fletcher and presenters Kate Garraway, Cherry Healey, Angela Scanlon and Anita Rani.
Dame Helen said: “Homelessness on our streets is a real problem in the UK and for many nations throughout the world. This coupled with an unprecedented number of refugees being displaced internationally makes this a really important time to focus attention on the issue of global homelessness.
“The World’s Big Sleep Out campaign will play an important role in shining the political spotlight on the issues of homelessness and displacement whilst raising considerable funds to make a big difference.
“I am pleased to have this opportunity to make a contribution by performing a bedtime story for participants in London, which will also be screened at sleep out events happening throughout the world.
“I’d like to encourage anyone who cares about this issue to get involved by sleeping out, in solidarity with those who have no choice, on 7 December.”
The World’s Big Sleep Out was spearheaded by Josh Littlejohn, who said he was “blown away” by the response so far.
“It doesn’t matter if you are taking part in Times Square or in your back garden with your family, by sleeping out for one night on 7 December we can simultaneously express our compassion for homeless people who have no other choice and raise lifesaving funds to make a difference,” he said.
“We can also send a message to the world’s political leaders that urgent action is required to address the human suffering that we each witness on our streets every day.”
A new charity called The World’s Big Sleep Out Trust has been established to govern the funds raised from the global event, while funds raised in the USA will be managed by Unicef USA with the support of Robin Hood Foundation.
Research by the Institute of Global Homelessness shows that there are more than 100 million people homeless and displaced around the world.
The event takes place on 7 December. People are urged to register for an official event or sign up to “Host Your Own” sleep out in their backyard, office car park, high school or university campus by visiting bigsleepout.com.
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