LONDON, March 27 (Reuters) - Tom Hayes, the first trader jailed worldwide for interest rate rigging, lost his appeal against his conviction in a London court on Wednesday.

Hayes, a former star Citigroup and UBS trader, was convicted in 2015 of conspiracy to defraud by manipulating Libor, a benchmark rate once used to price trillions of financial products globally.

Prosecutors said Hayes and other traders were acting illegally by taking their or their employer's commercial interests into account when they made submissions on the London interbank offered rate (Libor).

Hayes, who was released from prison in 2021 after serving half of an 11-year sentence, has always said that the Libor rates he requested fell within a permissible range – and that his conduct was common at the time and condoned by bosses.

His appeal against his conviction was heard alongside that of Carlo Palombo, a former Barclays trader convicted in 2019 of skewing Libor's euro equivalent, Euribor.

Their cases were referred to the Court of Appeal in London after a landmark U.S. court decision in 2022, in which two former Deutsche Bank traders' convictions for Libor rigging were overturned.

Hayes and Palombo's appeals were dismissed, senior judges announced on Wednesday after a hearing which began last week. The decision can be appealed to the Supreme Court. (Reporting by Sam Tobin)