Leading Democrats made a renewed drive on Thursday for a “public option” as a Senate panel scheduled a key vote on its pivotal $829bn reform plan next Tuesday.

Nancy Pelosi, the Democratic speaker of the House of Representatives, also floated the idea of a windfall tax on health insurers on Thursday, sparking a drop in the share prices of companies in the sector. The hardest hit was Wellpoint, the biggest insurer by enrolment, which dropped $2.94, or 6.2 per cent, to $44.72.