It depends on the fare you bought. Like airline pricing, sleeper fares come in different types with different rules. The cheapest, advance-style fares are usually non-refundable if you simply change your mind, though you can often amend them for a fee plus any difference in fare; more flexible (and more expensive) fares generally allow changes and refunds with fewer restrictions. If a train is cancelled or significantly delayed, you're entitled to a refund or to be rebooked under the usual passenger rights, separate from the fare conditions. The safest approach is to check the specific conditions attached to your fare at the point of booking — they're shown before you pay — and to keep your booking reference handy. For changes, contact the operator (Caledonian Sleeper or GWR) as early as possible, since options narrow closer to departure. Travel insurance can cover cancellations for reasons like illness that the fare rules won't. Because terms vary by fare and can change, always read the conditions for your exact ticket rather than assuming, and don't leave a change to the last minute.
Sources: sleeper.scot · gwr.com
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