Greenpeace activists have climbed to the roof of HP’s Californian headquarters and scrawled ‘Hazardous Products’ in non-toxic finger paint.

The environmental organisation said it wrote the inscription, which is over 1000 metres square, after the company postponed its 2007 commitment to stop using dangerous substances such as PVC plastics and toxic flame retardants in its products by 2009. Employees were also flooded with automated phone calls from Star Trek actor William Shatner urging them to phase out the substances.

HP said it was “a leader in environmental responsibility” and described the incident as “unconstructive antics”, insisting it was already reducing the use of brominated flame retardants (BFRs) and PVC materials in its products and aimed to be free of them by 2011.

“HP is a worldwide leader in e-waste recycling,” the computer manufacturer said. “HP has recycled 1 billion pounds of electronic products from 1987 to 2007 and has committed to recycling another billion pounds between 2008 and 2011."

Greenpeace’s actions follow a report it issued ranking various electronics vendors according to their e-waste elimination commitments. Apple was ranked highest while HP shared the bottom rungs with Lenovo and Fujitsu.