The 74 -year-old stood on top of the white tank as it arrived outside the PM's house in Dean, Oxfordshire.
Westwood declared: "Cameron plans to force householders to surrender their land and endure fracking underneath their homes. Britons no longer have any choice but to fight back", she told the BBC.
Cameron was in Yorkshire at the time of the protest and the Department of Energy and Climate Change said in a statement it forbids hazardous fracking operations.
The demonstrators, including a group of grandmothers and their grandchildren from Lancashire criticised the 27 licences issued in the North and Midlands.