In the article there were direct quotes by hostages who gave their names. Are you calling them liars?
No. But British newspapers in general aren't as careful as ours, and the Daily Mirror is bad all around.
The main thing is that these terrorists are as evil as evil can be. However, what commonly happens in these cases is that the exact form the evil took gets misstated. The danger is that people looking for excuses to look the other way then start to mistrust all the reports. The classic example was the Belgian attrocities committed by the Germans at the start of World War I, when they killed many thousands of Belgian civilians. Sometimes they just went after the priests, but more than once they locked the whole village in a building and burnt it. This is in the recent book "The Rape of Belgium."
Unfortunately, the Belgians started claiming, among many true horrors, one apparently false one -- that babies were bayoneted. Actually, although the Germans would shoot or burn anyone, it just was not true that they singled out babies for extra savagery or special measures. As a result, after World War I, the "lie" about the bayonetted babies was constantly trumpeted as proving that the Germans weren't as bad as extremists like Churchill said they were.
The historical lesson here is that it pays to just emphasize the horrors we know to be true. No matter how good a story sounds in the Daily Mirror, which is, after all, leftist, I see no reason to repeat it until it appears elsewhere and plenty of reason to be careful.