The portal wars in the UK are heating up, as CoStar-owned portal OnTheMarket (OTM) fights accusations of using “misleading” traffic data to dethrone competitor Zoopla as the second-most trafficked home search site in England, Scotland, Wales and Northern Ireland.

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The portal wars in the UK are heating up, as CoStar-owned portal OnTheMarket (OTM) fights accusations of using “misleading” traffic data to dethrone competitor Zoopla as the second-most trafficked home search site in England, Scotland, Wales and Northern Ireland.

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A Zoopla spokesperson spoke to international proptech site Online Marketplaces on Monday with allegations that OnTheMarket used “low-quality display advertising” to boost its website traffic to 56 million visitors in September and mislead consumers into believing OTM had organically surpassed Zoopla, which had 47 million visitors during the same period.

“While we typically avoid engaging in public debates, we believe it’s important to share the facts so you can better understand the claims and tactics being deployed to ‘Win your appreciation,'” Zoopla said in a written statement.

Zoopla said OTM’s September traffic spike is ultimately a blip on the radar, as Zoopla has outperformed OTM every other month of the year. The portal also cited data from third-party traffic analysis site Similarweb that noted OTM’s visitor duration and page views per visit declined 9.8 percent and 20.8 percent, respectively, in September despite a 209 percent boost in paid traffic.

“OTM’s strategy seems to be focused on increasing traffic numbers rather than engaging serious movers,” Zoopla added.

Meanwhile, OTM was unfazed by Zoopla’s claims and reasserted its newfound position in the UK portal space.

“We are grateful to Zoopla for highlighting that more people visited OnTheMarket than their site,” an OTM spokesperson said in a written statement. “Since CoStar Group’s acquisition, we’ve been clear about our goal to become the UK’s market-leading portal.”

“Our rapid rate of growth shows that we are delivering on CoStar Group’s long-standing strategy of partnering with its customers to generate high-intent leads at a fraction of the cost of our rivals,” they added. “The facts are clear that throughout 2024 we have seen a huge increase in leads, time spent on the site, and overall traffic, exceeding Zoopla’s in September.”

The burgeoning rivalry between OTM and Zoopla mirrors the ongoing row between CoStar-owned Homes.com and Move-owned Realtor.com, which have spent much of the past year tussling over claims of misleading traffic metrics, deceptive advertising and theft of trade secrets.

In October 2023, CoStar drew heat for announcing that Homes.com had achieved 117 percent unique visitor growth from August (46.3 million) to September (100 million) — apparently vaulting the site ahead of Realtor.com as the second-most trafficked portal in the U.S. However, Homes.com’s competitors quickly raised issues with CoStar’s reporting methods, traffic monitoring tools and other strategies to boost performance, such as an aggressive paid traffic strategy.

“It’s difficult to understand the consistency of their calculations,” a Realtor.com spokesperson told Inman in a 2023 deep-dive on portal traffic.

The traffic battle evolved into 2024, with Homes.com’s traffic performance serving as the basis for Move’s National Advertising Division challenge and theft of trade secrets lawsuit against CoStar. The NAD challenge led CoStar to adjust its advertising to focus on Homes.com’s singular traffic metrics over Homes.com Network traffic performance, while the theft of trade secrets suit is on track for an August 2025 jury trial.

Email Marian McPherson

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