The 24-year-old woman, who calls herself "Greta", is the last of 20 demonstrators who occupied a camp in a small wood outside the gates of Huntingdon Life Sciences chemical research centre near Huntingdon, Cambs. Bailiffs and police moved in to clear the camp early on Tuesday after HLS obtained a High Court eviction order last week.
Several demonstrators had to be cut free after chaining themselves to iron blocks embedded in the ground or attaching themselves to a tree.
Greta, who says she has water but no food, moved into the 5ft by 3ft steel safe when bailiffs arrived and said she would move into an underground tunnel if need be.
Cambridgeshire Under- Sheriff Herbert Robertson said his staff were working slowly to ensure that she was not hurt. Oxygen was being pumped in.
The laboratories have been a target for the animal rights movement for many years.
There has been renewed focus on the company since a Channel 4 documentary in March.
Two workers, who have now left the company, admitted cruelty and were given community service orders by magistrates as a result of the documentary.
The Home Office has warned the company that it could lose its licence if standards were not improved.Reuse content