Blair's discreet, then public, talks to bring Gadhafi into the international fold in 2004 were initially met with discomfort in Britain, amid memories of the Lockerbie air disaster, when Libyan agents brought down a Pan Am airliner over Scotland in 1988, killing 270.
The decision to travel to Tripoli and shake hands with Gadhafi in a desert tent in 2004 was "highly controversial, but it was the right thing to do," Blair's official spokesman said while speaking on condition of anonymity in line with government policy.
Libya had since made good on a 2003 promise to scrap its weapons of mass destruction program and plays a "useful role" in pan-African moves on climate change and Darfur, he said.
Blair, accompanied by his wife Cherie, planned to hold talks with the Libyan leader Tuesday, intended to cement ties on weapons decommissioning and counterterrorism.
Britain is also pursuing new economic ties with Gadhafi's regime, Blair's spokesman said. BP PLC was due Tuesday to announce a new project in the country, he said, without giving details.
BP PLC said it was in "constructive talks with the Libyan government," but would not release further details of a planned deal ahead of a formal announcement.
Since renouncing his nuclear weapons program in 2003, Gadhafi agreed to scrap his chemical weapons stockpile by the end of 2010. British experts are aiding the work and helping Libyan weapons scientists turn their expertise to radiological medicine, the Foreign Office said.
In turn, Tripoli cleared hurdles for Britain to deport suspected Libyan terrorists back to their homeland, signing a 2005 "memorandum of understanding" with Britain in 2005, a legal document promising not to torture the men.
But the policy was dealt a severe blow in April, when an appeal judge rejected the legality of the assurances, upholding claims from two Libyans that they could face violence if deported. Both men were ordered to be freed from custody.
The British government is aware of concerns about human rights in Libya and doubts over the systems of government and justice, but believes it is crucial to continue developing ties.
"Do you get change by standing on the sidelines or by engaging with such countries?" Blair's spokesman said.
Blair hoped to use the tour - which will also include visits to Sierra Leone and South Africa - to corral support for greater pressure on Sudan over the Darfur bloodshed.
"We need to go further at the U.N. and further on issues such as no-fly-zones," Blair's spokesman said.
U.S. President George W. Bush was announcing stiff new economic sanctions against Sudan Tuesday and also planned to call for a new U.N. resolution.
Talks in Sierra Leone, where British troops were deployed from 2002-2004, would mark upcoming July elections, the first since U.N. peacekeepers left, Blair's spokesman said.
Blair and South African President Thabo Mbeki planned to discuss action on Zimbabwe and U.N. Security Council issues, including climate change, at talks in Johannesburg, the spokesman said.