Italy and India are working themselves into a diplomatic quarrel that both may regret

When a friend behaves badly, it's easy to take a time out. Stop taking their phones calls, pretend to be out when they come to apologise.

But responsible nations don't have the luxury of ignoring each other. That is why diplomacy can be a messy business, as India and Italy are learning this week.

In February, the Indian Supreme Court ruled that two Italian marines charged with murder in international waters off Kerala could return home to vote. At the time the Italian ambassador, Daniele Mancini, gave a written promise that they would return.

But then on Monday Rome told New Delhi the marines would not be returning after all, arguing that India does not have jurisdiction. New Delhi responded by barring Mr Mancini from leaving the country.

India is clearly stung by the Italian double-cross; Prime Minister Manmohan Singh has warned of "consequences"should the marines fail to return. No doubt Mr Singh understands the populist pulse that drives Indian politics.

He didn't say what those consequences might be, but we can guess. Italy is a key trade partner for India, and annual bilateral trade increased by 18 per cent last year, reaching €8.52 billion (Dh40 billion). Should this spat escalate, odds are diplomats won't be the only ones feeling the squeeze.