The FTSE 100 Index is down 41.5 at 5136.9 after an hour's trading, ending three sessions of rises.
Banking and oil stocks are weighing on the market, pushing the index back down towards 5,100.
The falls come after a mixed session last night on Wall Street, where the Dow Jones Industrial Average gained but the Nasdaq fell on downbeat news from Cisco.
Royal Bank of Scotland is down 2 per cent or 29p at £17.05, despite reporting profit figures above expectations and saying integration benefits from NatWest will be higher than planned. But the group has also increased its provision for bad debts.
Other fallers include HSBC, off 17½p at 779½p; Barclays, down 31p at £20.94; and HBOS, off 5p at 735p.
HBOS, which yesterday announced a £1.37 billion share placing, said it has placed 150 million shares at 740p.
PA