What to do about the threat posed by Isis, also known as Islamic State, is now a question exercising the minds of military planners and policymakers in Westerns capitals. 

A Saudi-led military force crossed into Bahrain to prop up the monarchy in the tiny island nation against widening demonstrations, launching the first cross-border military operation to quell unrest since the Arab world’s rebellions began in December.

Dubai was waiting today to see whether neighbouring Abu Dhabi would bail out the credit-crunched city-state.