The FTSE-100 index was down 60.01 points to 6078.68 at 9.15am, as RBS, Barclays and Lloyds suffered falls in their share value.
ITV News Business Editor Joel Hills has the latest:
Look past headline FTSE100 number. UK bank shares RBS -12%, Barclays -9.5%, Lloyds -9% following downgrade by - erm - Barclays analysts.
Joe Trundle, Head of Trading at ETX Capital, said: "Banks are being hammered as a result of Britain’s decision to leave the EU. Aside from the general investor uncertainty, there are some important reasons why financial stocks are so exposed.
"First, there is a realisation that interest rates will remain low for longer – gilts have sunk below 1% for their first time ever today. This is not confined to the UK - Australia’s central bank may have to cut rates because of the vote.
"Second, property assets will have to be revalued and that could severely dent banks’ loan books.
"Thirdly, British banks probably won’t have access to EU markets post-Brexit as they’ll lose their 'passporting' privileges.
George Osborne has said the UK economy is "prepared for the unexpected". So did he overstate his Brexit warnings?
Chancellor George Osborne will seek to reassure financial markets on Monday morning following Britain's decision to leave the EU.
Soros says that the European Union will struggle through the process of Brexit, with other countries wishing to follow suit.