London's Metropolitan Police force urged the group to reconsider, saying the airport action could "cause further disruption and misery to thousands of travelers, many of them families, over Easter."Protesters can expect a robust police response", said Assistant Commissioner Nick Ephgrave".
Prior to appearing at the protest, Thompson shared a video to explain the importance of the protest and what Extinction Rebellion hopes to accomplish, declaring herself "a climate change activist, have been for decades".
The Love Actually actress also challenged critics who have said demonstrators are using the protests to have fun.
Earlier, on Friday morning, about 20 activists, majority under 17, had staged a brief demonstration on roads near Heathrow Airport.
The protest is part of wider demonstrations around London.
Heathrow previously said it was "working with authorities" to remain business as usual.
Lesley Sweet, the first from the group who was arrested live on national television on Tuesday afternoon from Waterloo Bridge said: "We are facing the sixth mass extinction and it is now that we have to act".
Home Secretary Sajid Javid, Britain's interior minister, condemned the demonstrations saying protesters "do not have the right to break the law and significantly disrupt the lives of others".
The people charged are Cathy Eastburn, 51, from Lambeth, south London; Mark Ovland, 35 of Somerton, Somerset; and Luke Watson, 29, of Manuden, Essex.
Mr Marsh said the protests will cost millions of pounds and local communities will suffer.
XR has pledged to continue causing disruption until its demands are met.
Dame Emma clearly didn't see any hypocrisy in her actions as she took to the streets for the second time today, addressing protesters from a large pink boat and reading a poem called "Mother Earth Is Not Your Slut".