A British couple have told of their surprise after they discovered a man and woman having sex in the cabin they had booked for a £4,800 week-long cruise.

Mary and Bobby Jackson, 62 and 64 respectively, had booked a dream trip with Norwegian Cruise Line to take them from Singapore to Thailand before they returned home to Carrickfergus in County Antrim.

They got on board the ocean liner Jewel and made their way to their suite, only to find that the key card wouldn't work on the first two attempts, the Sun reports.

Perhaps this was fate's way of telling them to stay on the other side of the door - because on the third go, it swung open to reveal two strangers in flagrante on the luxury bed.

"I was horrified, what I witnessed was extremely unpleasant. I immediately closed the door again," said Mary.

"We are not prudes but this was ridiculous. I was traumatised and I needed a glass of water," she added.

To make matters worse, the woman immediately left, but the man remained in the cabin and was still there looking sheepish when the couple returned with some of the ship's crew.

And because the cruise ship was fully booked, there was no alternative cabin to offer the couple - let's just hope the sheets were at least changed before they were expected to bunk down there.

It's thought the male half of the couple was actually another member of Norwegian staff who has probably not been invited back, but the woman remains unknown.

Norwegian said a full investigation has now taken place and the "appropriate action" has been taken, including contacting the Jacksons to discuss compensation.

Well, at least it goes to show that cruise ships are romantic places on which to book a break if you fancy a change from the standard missionary in your own bedroom.