Tom Hayes Terry Farr James Gilmour
Tom Hayes (L), Terry Farr (C), and James Gilmour (R) all plead not guilty to the SFO's fraud charges under its Libor manipulation probe Reuters

Three men accused of conspiring to manipulate the key benchmark rate Libor have pleaded not guilty at a London court.

Former UBS and Citigroup trader Tom Hayes and two former RP Martin brokers Terry Farr and James Gilmour appeared at a plea hearing on 17 December.

Hayes has been charged with eight counts of fraud by the Serious Fraud Office (SFO). Gilmour is charged with one count and Farr two.

The three are the first to face trial under the SFO's probe into Libor manipulation since the scandal broke out in 2012.

Libor, or the London Interbank Offered Rate, is a series of daily interest rates calculated from submissions by banks of what rate they can borrow at from other financial institutions over certain periods of time, such as one month or three months.

Allegations surfaced that some traders and rate submitters had worked together to manipulate rates up or down by giving misleading or false submissions to Libor calculators.

The various Libor readings are used as benchmarks for financial products across the world's markets, from mortgages to interest rate swaps.

Following various probes by global authorities and regulators, banks have been hit with billions of pounds in fines.

Eight banking giants were fined a combined total of €1.71bn
(£1.5bn, $2.35bn) by the European Commission for rigging Libor and similar rate Euribor.

Barclays, Deutsche Bank, Société Générale, RBS, UBS, JPMorgan, Citigroup and RP Martin were part of two separate illegal cartels which conspired to manipulate Euribor and Libor to benefit their own positions in euro and Japanese yen-denominated interest rate derivatives markets.