The office said the site would make it possible for the Prime Minister or a minister to respond without having to pay for postage and packaging.
But the Sheila McKechnie Foundation said it hoped the new method of campaigning would complement the old one, not replace it. "Given the rising influence of e-campaigning, it is good Downing Street has responded in this way," a spokesman said. "We hope it will also continue with the tradition of allowing the physical handover of paper petitions.
"Photocalls of petition handovers at Downing Street have given grass-roots campaigners a visibility in their regional media they would otherwise lack."
The office said that paper petitions would still be accepted, but campaign groups would have to choose one method or another.