FTSE 100 hit by banks to close 5 pct lower

* FTSE 100 slides 5 pct, lowest close for over a month
* Banks hammered on credit outlook, sector down 10 pct
* Miners, oils down as commodity prices fall

By Simon Falush
LONDON, Jan 14 (Reuters) - Britain's blue-chip shares tumbled 5 percent to their lowest close in over a month on Wednesday led by financials which were thumped on anxiety over their balance sheets.