Conservative leader David Cameron and shadow foreign secretary William Hague are in Iraq on a fact-finding visit.
David Cameron: A fact-finding visit
The pair are visiting UK troops based in the southern city of Basra.
Mr Cameron was due to speak at the CBI business conference in London, but shadow chancellor George Osborne took his slot on the platform.
Foreign Secretary Margaret Beckett announced last week that security of the Basra area could be handed over to Iraq forces by next spring.
Mr Cameron said: "The situation in Iraq is one of the most critical issues facing the British government and our country."
He said he wanted to show his support to troops and hear their experiences.
He also said he wanted "to get a more direct understanding of the political situation by meeting Iraqi politicians and to look at the prospects for halting the terrible cycle of violence and for making the transition to Iraqi control over security".
Back in London, Defence Secretary Des Browne is stressing that although handing over security in the spring will mark a "decisive change" for Britain's role in the country, it will not mean all British troops leaving Iraq.
Instead, a substantial number are expected to be based outside Basra, available to help with security if needed.
Mr Cameron's absence from the CBI conference on Monday "disappointed" organisers.
CBI president Sir John Sunderland, said: "It would have given him a chance to address some of the uncertainties about his position on a number of important business issues, so we see this as a missed opportunity."
A Conservative Party spokesman said the situation in Iraq "is currently one of the most pressing issues that faces the country and it is essential that David Cameron, as leader of the Opposition, is fully informed of the situation on the ground".
He rejected any suggestions of a snub to the CBI, pointing out that Mr Cameron addressed the annual dinner of the Institute of Directors last week, spoke at the CBI's annual conference last year and had recently addressed the President's committee of the CBI.
Chancellor Gordon Brown visited British troops in Basra earlier this month.