According to three top scholars interviewed by the BBC News website, jihad can only be called in the following circumstances:
*If a Muslim community comes under attack, then jihad becomes an obligation for all Muslims, male and female, in that community
*If that particular community feels it cannot fight off attackers on its own, then jihad becomes incumbent on Muslims living in nearby communities
*If a Muslim ruler of a country calls for jihad, then it is incumbent upon the Muslims living under that ruler to join the jihad.
Mufti Usmani says that even in such circumstances, jihad is obligatory only on as many Muslims as are required to defend the community under attack.
"If Pakistan is attacked but its army is sufficient to deal with the threat, then Pakistani civilians are under no obligation to join jihad," he said.
The second principle relates to the conduct of the jihadis. Under no circumstances are Muslims allowed to attack women, children, the old and the meek, the sick, those that are praying and civilians, say these ulema.
Muslim militants argue that if innocent Muslims are killed in enemy action then Muslims are allowed to kill innocent people in retaliation.
But clerics strongly disagree with this line of thinking, arguing that Islam does not allow Muslims to respond to "a mistake" by another mistake.
"Islam is absolutely clear on this issue. Two wrongs do not make a right," Mufti Usmani said.
"If they feel that the US or the UK are killing innocent civilians in Iraq or Afghanistan, it does not give them the right to kill innocent citizens in London or New York," he said.
Dr Sikander, who heads Jamia Binoria in Karachi, says the Muslims have their options clearly cut out under Islam if they do not agree with the foreign policy of those countries where they are living...
...Dr Sikander says that should Muslims feel that their country of residence is doing something terribly wrong, then all they can do is to leave the country.
"If an Iraqi living in London is outraged over Britain's role in what is happening in Iraq, then he should go to Iraq and fight the coalition forces there," he said.
"Nothing gives him the right to hit back at innocent civilians living in the UK."
Pakistani clerics say that the doctrine evolves from the fundamental Islamic principle of honouring commitments.
"When a Muslim visits a Western country or if he is living there, then he is under a kind of a contractual obligation to abide by the law of that land," explains Mufti Usmani.
"Islam is so strict about honouring commitments that a commitment cannot be revoked unilaterally even in times of battle."
A very good summary.
12:05:50 AM 
