A morning-after headache may be the side effect of a pint of plain and a whiskey chaser but at least it’s short-lived — the long-term hangover is the thousands of tonnes of carbon emitted during production.

Guinness bosses today raised their glasses to a record one million visitors who have flocked to the home of the black stuff so far this year.

More than 400 Irish farmers today protested outside the historic Dublin headquarters of Guinness over prices they are receiving for malting barley.