European Highlander is more or less confirmed as not returning until Wednesday. P&O have posted to twitter a 4 sailing timetable for Monday and Tuesday:
"Revised schedule for Monday & Tuesday; Ex Larne - 0730, 1330, 1930, 0130 Ex Cairnryan - 1030, 1630, 2230, 0430. Call 0845 839 845 for update"
Passengers expecting to travel with P&O over the next few days are advised to contact P&O for the latest information.
Meanwhile, Stena Superfast VII may return from Harland & Wolff early tomorrow evening. She had originally been expected to return on Tuesday morning. Express has left Belfast and is now at Larne. Her season operating to Troon begins on Monday 31st of March.