The Obama administration was on Tuesday scrambling to contain a growing backlash from liberal Democrats that could prove fatal to his hopes of pushing through healthcare reform.

In a letter to Kathleen Sibelius, the secretary for health and human services, 60 Democratic lawmakers in the House of Representatives warned that they would vote against healthcare reform if it excluded a public insurance option that would provide a state-run alternative to private insurance plans for low-income people. That would leave Mr Obama needing 22 Republican votes in the lower chamber – a very tall order.