The owner of the property website OnTheMarket has secured a victory in the Competition Appeal Tribunal after it ruled that a Cheshire-based estate agent breached its contract when it advertised its properties on rival websites Zoopla and Rightmove.

Agents’ Mutual, which is owned by a number of estate agents including Savills and Knight Frank, claimed that estate agency Gascoigne Halman broke a condition of its membership when it listed its properties on Zoopla and Rightmove. The agreement stated that in order to use its website, all estate agents were allowed only to list properties on their site and one other competing portal.

Gascoigne Halman argued that the “one other portal” rule was anti-competitive and that it amounted to a collective boycott of rivals.

Eversheds Sutherland partner Lesley Farrell acted for the claimants, instructing Blackstone Chambers’ Alan Maclean QC and Monckton Chambers’ Josh Holmes QC; while Quinn Emanuel Urqhuart & Sullivan partners Boris Bronfentrinker and Kate Vernon acted for the defendants, instructing Paul Harris QC and Philip Woolfe QC at Monckton Chambers.

Mr Justice Marcus Smith ruled that Gascoigne Halman’s case was “untenable” and rejected it. He said: “For the reasons we have given, in some circumstances horizontal co-operation even between competitors can be perfectly acceptable in competition terms; and the use of exclusivity requirements – like the One Other Portal Rule – can, as we have found, be similarly acceptable, either because competition law is not infringed at all (as here) or because an anti-competitive restriction is objectively necessary (as we would have found, had our conclusions on “by object” and “by effect” infringements been different).”

Smith J continued: “It would appear inherently plausible that, all else equal, the entry of a new portal would be pro-competitive in that estate agents would have an additional or alternative portal on which to advertise their properties; and the property buying public would have an additional or alternative portal through which to view such properties.”

Farell said: “Gascoigne Halman had claimed that a number of the terms within OnTheMarket’s agreements with agents listing on the portal were anti-competitive. We are very pleased that the Competition Appeal Tribunal has determined, unanimously, that there is no basis for those claims and that the agreements are in fact ‘pro-competitive’.

Agents’ Mutual CEO, Ian Springett, added: “The aim of our portal has been to increase competition and choice for estate agents and property seekers. I am delighted that the Competition Appeal Tribunal has recognised that OnTheMarket’s entry into the online property portal market is pro-competitive and that, in accordance with the advice we had been given, the terms it has with its agents are compatible with competition law. ”