Egyptian security forces are on high alert, with thousands of people expected to join anti-government rallies after Friday prayers.
The protests have led many international leaders to call on President Mubarak to loosen his hold on power.
But for Middle East envoy Tony Blair, while he is "absolutely in favour of change" in the country, the process has to be conducted "very, very carefully".
"If you open up a vacuum anything can happen," he told Justin Webb. "The question is how they evolve and modernise".
This is an extended version of the broadcast interview.
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