With the British government expected to approve the airport expansion this week, Greenpeace says its move is meant to put legal hurdles in the way of the project, hoping that the longer it is delayed, the more likely it is to be canceled, The Times of London reported Tuesday.

The newspaper said the field, about the size of a soccer pitch, will be used by Greenpeace to dig a network of tunnels and will be subdivided into tiny plots with separate owners so Heathrow owner BAA would be forced to enter into time-consuming negotiations with each owner.

British actress Emma Thompson was among those who signed the deeds to the site late last week, The Times said.

"I don't understand how any government remotely serious about committing to reversing climate change can even consider these ridiculous plans," she told the newspaper. "We'll stop this from happening even if we have to move in and plant vegetables."