"The director of the Serious Fraud Office has today opened a criminal investigation into allegations of fraudulent conduct in the foreign exchange market," it said in a statement, without giving further details.
EU, British, and US and other regulators have levied huge fines on some of the world's biggest banks and investment houses for manipulating currency markets worth trillions of dollars.
In June Britain's government, the Bank of England and financial regulators proposed legislation to punish foreign exchange rigging with criminal sanctions.
Some traders have been found guilty of manipulating the Libor and Britain has already threatened prison for those found guilty of rigging it.
The Serious Fraud Office had previously said that it was looking at "complex" evidence before deciding whether to launch an inquiry.