Was the petrol price rigged too?

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Petrol retailers use oil price "benchmarks" to decide how much to pay for future supplies.

The rate is calculated by data companies based on submissions from firms which trade oil on a daily basis -- such as banks, hedge funds and energy companies.

However, like Libor -- the interest rate measure that Barclays was earlier this month found to have rigged -- the market is unregulated and relies on the honesty of the firms to submit accurate data about all their trades.