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Last Friday brought investors in Rightmove

a new and unwelcome experience — a violent stock price correction.

Shares of the U.K.’s biggest property portal, which hit a record in late July, fell by 28% at one point before finishing 12.5% lower, clipping nearly £634 million ($833.4 million) from Rightmove’s stock market valuation.

The sell-off followed a trading update in which the former stock market darling, which accounts for more than 70% of all consumer time spent on U.K. property portals, pledged to hike spending on artificial intelligence at the expense of short-term profit growth.