The Egyptian Army had to intervene to remove President Mohammed Morsi or face "chaos" amid protests by millions, former PM Tony Blair has said.
He told the Observer no UK government would have survived such an "awesome manifestation of people power".
But Tory Lord Hurd said Mr Blair had "rushed to judgement" and the outcome may not be known for months or years.
The army removed Islamist leader Mr Morsi, Egypt's first democratically elected president, last week.
It followed mass protests against his government - elected following the 2011 revolution and the overthrow of former president Hosni Mubarak.
Mr Blair - now a special envoy to the Middle East - wrote: "I am a strong supporter of democracy. But a democratic government doesn't on its own mean effective government."
When governments did not deliver, people did not want to wait for an election. And in Egypt the economy was "tanking", law and order had "virtually disappeared" and services were not functioning properly, he said.
"The events that led to the Egyptian army's removal of President Mohammed Morsi confronted the military with a simple choice: intervention or chaos," he wrote.
"Seventeen million people on the streets are not the same as an election. But it as an awesome manifestation of power.
"The equivalent turnout in Britain would be around 13 million people. Just think about it for a moment. The Army wouldn't intervene here, it is true. But the government wouldn't survive either."
Mr Blair said the world must "engage" with the interim government to help it make economic reforms because we "can't afford for Egypt to collapse".
'Rock and hard place'
One positive development was there was an "open debate about the role of religion in politics" and "probably a majority for an intrinsically secular approach to government in the region".
In a BBC interview on Thursday, pro-reform leader Mohamed Elbaradei said the army had not "taken over" - it had been asked to intervene by millions of protesters: "The other option was civil war, we were between a rock and a hard place."
But Lord Hurd, a former foreign secretary, told the BBC's Andrew Marr Show Mr Blair "leaps in before he's thought things through" and it was important not to "rush to judgement".
"The seizure of power by the military was the second act in a drama that is going to go on and on and on.
"We won't know for weeks, maybe even months, whether the military... have made a good gamble for Egypt or bad."
"We should not go out of our way to clap our hands and say: 'That's marvellous,' as Tony Blair has done. We should keep our counsel, keep our wits about us, and wait for the last act of the drama which may be some years away."
But Foreign Office minister Alistair Burt said it was "certainly a different form of military intervention than that conventionally expected".
"It is a very difficult political process there and the military engagement in trying to, in a way, hold the ring, being worried about security and violence, is very clear.
"But what they must not do now is they must not demonstrate by their actions that they are trying to take sides in a future election - they should release those who have been arrested for political reasons if they've not been involved in inciting violence or anything like that."
Meanwhile, earlier reports that Mr Elbaradei had been appointed as interim prime minister were corrected by interim president Adly Mansour, who said consultations were continuing.
The news had been criticised by the Salafist Nour Party, Egypt's second-biggest Islamist group, which said it would not work with him.