Refunds under Condition 30.1 of the National Rail Conditions of Travel are available in the normal manner in the event of cancellation due to industrial action, with the explicit exception to the normal policy where only the Return leg of a Return is affected, where you're entitled to a refund of 50% of the ticket price rather than merely the difference in price between the Single and Return (which could potentially be as low as 5p). With Advance tickets, the refund request can be submitted before the day of travel or up to 28 days after the original day of travel.