You Can't Understand Just How Big The Tesco Disaster Is Until You See How It Once Dominated Britain

British grocery chain Tesco is the country's biggest supermarket, Europe's largest private employer, and world's second-largest retailer - second only to Walmart.

And it's a total basket case.

After revealing in late September that it overstated profits by £250 million, the grocer revised that number upward today to £263 million, culminating in the resignation of Tesco's chairman, Sir Richard Broadbent.

Tesco's new CEO Dave Lewis has been left to pick up the pieces, while at the same time dealing with a separate but equally massive problem: disastrous global sales results. The share price has dropped by more than half in the last 12 months.

So what went wrong?