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See point 4.2 of the T&C here-
Flying Club Terms and Conditions | Virgin Atlantic
4.2.1 Once Reward tickets are issued, you may amend your travel date, route or class of service prior to travel for an amendment fee of £30 for changes to international flights originating in the UK, US$50 for changes to international flights originating in the US or local currency equivalent of US$50 for changes to flights originating in any other region. Where the Reward is a Companion Reward and the person travelling on the paying ticket changes his or her flight or class of travel, the Companion Reward may be similarly amended for the same amendment fees, subject to availability of seats and the provisions of section 4.4 of these Flying Club Terms.
Once tickets for a Rewards booking are issued, no name changes are allowed. If for any reason a flight Reward is cancelled by the Member outside 24 hours of departure, 100% of the Virgin Points will be re-credited to the Member’s account. A cancellation fee of £30 for changes to flights originating in the UK, US$50 for changes to flights originating in the US or local currency equivalent of US$50 for changes to flights originating in any other region will apply.
Nick