That overspend would have to stop immediately - far worse austerity than the troika demands. The Greek banks would also collapse, bereft of outside support.
Having crossed the Rubicon of unilateral default, many economists believe the Greeks would leave the euro altogether.
One reason is the need to devalue its currency to restore competitiveness. "Greece needs to move its exchange rate by at least 30% to have any chance of getting jobs back," says Mr Booth.
Another is that the Greek central bank could then fund the government's continued borrowing with freshly-printed drachmas. But inflation would soar, and imports especially would become very expensive
All you need to know about our national debt - please read problems of national debt bit
