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* Former RP Martin brokers Farr, Gilmour charged
* Follows SFO charging former UBS, Citi trader Hayes
* Interdealer brokers under scrutiny for middlemen role
LONDON, July 15 (Reuters) - Britain's fraud prosecutor onMonday charged two former brokers at interdealer broker RPMartin with conspiracy to defraud, stepping up its investigationinto the rigging of Libor benchmark interest rates.
The Serious Fraud Office (SFO) said it had charged TerryFarr and James Gilmour, seven months after arresting them. Theyare the first brokers to be charged in the Libor scandal.
The two were arrested a fortnight before Christmas alongwith former UBS and Citigroup trader Tom Hayes,who was last month charged with eight counts of conspiracy todefraud as the SFO laid the groundwork for what could be thefirst Libor trial.
A central cog in the world financial system, the Londoninterbank offered rate (Libor) is used as a reference for some$550 trillion in contracts ranging from complex derivatives toeveryday credit card bills.
Trust in the benchmark was shaken by revelations last yearthat traders had routinely manipulated it, prompting a series ofinvestigations by regulators and other authorities.
Britain's Barclays and Royal Bank of Scotland and Switzerland's UBS have been fined by U.S. and UKauthorities for manipulating Libor, and more banks andindividuals are under investigation.
Inter-dealer brokers were drawn further into the probe whenUBS admitted in its settlement in December that its traders paidbribes to brokers in return for their help rigging interestrates. The payments to unnamed brokers ran at 15,000 pounds($22,700) per quarter.
Farr, 41, and Gilmour, 48, will appear before WestminsterMagistrates' Court at a later date, the SFO said.
RP Martin declined to comment.
Brokers are the middlemen who match buyers and sellers for avariety of financial securities, such as bonds, currencies orinterest rate swaps. They speak to traders at banks daily,giving them a unique and privileged view of banks' trading.
RP Martin is a UK-based broker with offices in Europe,America, Africa and Asia, but is much smaller than rivals suchas ICAP and Tullett Prebon.
The firm traces its history back more than 100 years and isone of the oldest money broking businesses in the world,according to its website. It is known for specialising intrading foreign currencies, and was considered a big player inthe Swiss Franc market in the past.
The U.S. owner of the New York Stock Exchange announced last week that it would take over the running ofLibor, in a move that Britain's financial regulator said wouldrestore its integrity.
