According to our good friend ChatGPT:
No, a cancelled UK passport cannot be used for international travel — even if it is still within its original expiry date.
Here’s why:
🔒 What "Cancelled" Means
When a UK passport is cancelled (e.g. because a new one has been issued), it is officially invalidated in HM Passport Office systems. That means:
It may be flagged in border control databases.
Airlines and immigration officers will treat it as void.
It might be physically marked (e.g., corners cut, punched holes), but even if it looks normal, it’s no longer valid.
✈️ Consequences of Using a Cancelled Passport
Refused boarding by the airline
Entry denied at border control
Delays, detainment, or fines in some countries
Even returning to the UK may cause issues, as your identity/travel document is no longer valid