So what if Greece leaves the euro?

Acropolis, Greece
Acropolis, Greece

Okay, so all of Europe is alight, and there's panic over Greece perhaps leaving the euro, Spanish banks getting into trouble, and the great and good of the eurozone apparently not having much clue how to get out of the mess.

And it's all driving our stock markets downwards week by week. But what difference does it really make to the outlook for Britain's best companies?