"The [rebel] council is increasingly articulating a vision for a strong, stable, post-Gaddafi Libya, preparations for which are underway," Clegg will tell the British Council audience.
"We are determined to learn the lesson of Iraq - no matter where you are in the conflict, you should already be planning for the peace."
He will also promise that the freedom movements in Tunisia and Egypt will get continued support from the UK.
Clegg was expected to say: "It is increasingly common to hear what was once hailed the Arab Spring now compared to a long, uncomfortable Arab summer. The truth is: we cannot be certain exactly how things will pan out, but the direction of travel is set.
"Youth, technology, a lack of opportunity and inclusion - factors which have collided to create citizens who want more, who know more, who aspire to more but who are denied it at every turn, this year that tension has hit boiling point.
"I want to make it absolutely clear: the UK will not turn its back on the millions of citizens of Arab states looking to open up their societies, looking for a better life."
Meanwhile, the Syrian President has said he is "not worried" about security in his country and warned against any foreign military action against his regime.
Bashar al-Assad's speech came as he continued to face international condemnation for his security forces' crackdown on dissent.
Assad's interview with state-run television followed a call by the United States and its European allies for him to step down, and came hours after a diplomat said Assad's regime was "scrubbing blood off the streets" ahead of a UN visit.
"I am not worried about the security situation right now, we can say the security situation is better," Assad said, in his fourth public appearance since the revolt against his family's 40-year rule erupted in mid-March.
In a now-familiar refrain, Assad promised imminent reforms, including parliamentary elections by February, but insisted the unrest was being driven by a foreign conspiracy.
Assad warned against Libya-style military intervention, saying "any military action against Syria will bring repercussions that [the West] cannot tolerate."
-Independent, AP