Could you please explain the meaning of "have taken a slide"??????
So, while traditional British institutions have taken a slide, there's plenty of evidence to suggest that IKEA will keep going strong.
When you 'take a slide'...you go down. So, I would assume that he means that it means that traditional institutions are getting worse, or weaker...or even disappearing. However, IKEA is maintaining a steady course...or even an upward trend and improving. ;)