JPMorgan Chase’s London unit has been fined a record $48.6 million by Britain’s financial regulator for not properly separating client money from the firm’s own accounts.

An average of $8.6 billion wasn’t properly segregated by JPMorgan Securities in an error that went undetected for seven years, the Financial Services Authority said in a statement yesterday.

As much as $23 billion of client money held by the bank’s futures and options business wasn’t put in separate overnight customer accounts between 2002 and 2009, the FSA said.

The bankruptcy of Lehman Brothers Holdings, which roiled financial markets worldwide in 2008, forced the FSA to put financial companies on notice that they must properly separate client funds.

Lehman’s creditors filed more than $830 billion of claims and regulators worldwide are trying to unravel how money moved through its global units.