Raga Woods, 52, formerly Tessa Fothergill, was one of three women and four men who took part in a mass invasion of the site earlier this month, despite being named, along with 47 others, in a High Court injunction won by the Department of Transport. Mr Justice Alliott jailed the group for 28 days for contempt, but promised to consider releasing them if they agreed to abide by the injunction.
Javan Herberg, for the defence, told the court that Ms Woods, a mother of two, apologised for breaching the injunction.
'She feels passionately about the rights and wrongs, especially the wrongs of the construction of the M3 motorway on Twyford Down. She feels it is vital that people protest against the destruction of our natural habitat,' he said.
'However, she accepts that she should not have carried on in breach of an order of this court.'
Outside the court, Ms Woods punched the air in triumph before vowing to fight on. 'The destruction of Twyford Down is a symbol of what the Department of Transport will do unless we wake up. Our idiotic system of transport threatens all that maintains life,' she said.
Ms Woods is due to fly to Japan on Friday with her younger son, Sadhu, 14, to see the boy's father, Agar Noiroi, a zen buddhist monk.
The other six protesters - Jason Torrance, Philip Pritchard, Simon Fairlie, Robert Bear, Rebecca Lush and Emma Must - are expected to serve out their term.
Ms Woods, 52, founded Gingerbread, a national organisation for single parent families, in the early 1970s before moving on to environmental issues. She lives in Eastleigh, Hampshire, three miles from Twyford Down.
Of the others jailed last week, Jason Torrance, 22, is a full-time environmental campaigner from East Sussex. He was first arrested at Twyford in February last year when the Department of Transport built a bridge across Oliver's Battery.
Rebecca Lush, 21, is a local environmental campaigner from Winchester. She has been active at Twyford since last October.
Simon Fairlie, 42, is a stonemason by trade, but became involved in environmental journalism about two years ago. Eighteen months ago, he was appointed editor of the Ecologist magazine, in which he has written at length about Twyford. Emma Must, 27, who works as a children's librarian in Winchester and is a member of the Friends of Twyford Down, has been involved in the campaign since the beginning of the year.
Robert Bear, who is in his early forties, comes from south Somerset, where he campaigned against the activities of the large quarrying companies in the Mendip Hills. He has been involved at Twyford since February when stone from Whatley Quarry was transported to the M3.
Philip Pritchard, who is in his early twenties, was originally with Friends of the Earth in Oxford. He has been active at Twyford for six months.
An appeal against the terms of the DoT's injunction will be launched this week.
The National Union of Journalists will support an appeal by Margaret Lambert, a student photo-journalist who was covering the demonstration as part of a project and who is named on the injunction.Reuse content