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This has been the tale of two balconies.

The first was in Algiers yesterday when David Cameron saw the balcony from which President de Gaulle famously appealed to the masses in a 1958 tour aimed at fighting off bloody demands for Algerian independence.

Today in Tripoli, the prime minister passed the balcony in what was Green Square and is now Martyrs' Square, where Colonel Gaddafi equally famously addressed a million Libyans who were chanting his name.

This morning a new crowd gathered there as word travelled that a visitor had arrived unannounced.

"Welcome, Cameron. Welcome," they said.

These days complete secrecy and heavy security - armoured cars and police helicopters - are needed to minimise the risk to a prime minister visiting Tripoli: even one regarded as a liberator.

Last week the Foreign Office ordered British citizens to leave Libya's second city, Benghazi, after warnings of an imminent threat to Westerners.

Britain's answer is to help train police here as David Cameron told recruits at Tripoli's police training college that their job now was even more important than overthrowing Gaddafi.

The UN envoy to Libya has warned that the conflict in Mali risks spilling over here as guns and heavily armed rebels cross borders from one conflict zone to another.

I put it to the prime minister that this would convince some that outside intervention always makes things worse. He insists that this is wrong.

David Cameron wants people to remember what things were like before Gaddafi was overthrown.

He has secured a promise that police investigating the Lockerbie bombing could visit here to pursue their enquiries. The promise came from a man who was protesting against Gaddafi outside the Libyan embassy in London on the day PC Yvonne Fletcher was shot. Today that man - Ali Zidan - is Prime Minister of Libya.