President Obama: Now is time for US and West to lead

President Obama has become the first US president to address members of both Houses of Parliament.

He told them the world was in need of leadership, and said that for Britain and America this was a pivotal moment of challenge.

The president said the UK and US have "one of the oldest and strongest alliances the world has ever known".

On the crucial issue of Libya, however, there did seem to be a difference of tone at a joint news conference earlier on Wednesday.

While David Cameron said he wanted to turn up the heat on Colonel Gaddafi, President Obama warned against setting a timetable for change.

Nick Robinson reports.