If your return transport (flight, train, ferry etc) to the UK is cancelled while you are abroad your policy will automatically extend, providing you accept any alternative offered and do not intentionally delay your return.
If your provider does not offer you an alternative we would expect any alternative return transport you book to take place either later the same day or the next day unless you can prove that no alternative option was available within this period and that you took the first available option.
If you chose to extend your trip due to the cancellation of your return transport (intentionally delay your return) your policy will not automatically extend, we may be able to extend your policy duration for an additional premium. In most cases you will be able to do this online via your Customer Zone.