"Ladies and gentlemen, we will be delayed here for approximately 30 minutes while an engineer attends, however please do be aware that we could end up with the problem solved sooner than that, or it could take longer. If you leave the train, please therefore do not leave your luggage unattended[1], take it with you, for both security reasons and in case we get cleared to leave earlier, as we will not be able to wait for you in that case, and if left unattended it may be removed and destroyed[2]. If you hold an Advance or similarly restricted ticket, please note that if you do get off and the train goes, you will have to buy a new ticket. Thank you."
[1] See It, Say It, Sorted points there
[2] More SSS points