The ‘one other portal rule’ was the best and most realistic opportunity for OnTheMarket’s entry into the property portal market, the Competition Appeals Tribunal has heard.

But it also heard – from the QC representing agent Gascoigne Halman – the rule described as defensive and protectionist.

The hearing is examining competition issues over the ‘one other portal’ rule, with arguments being advanced by both Agents’ Mutual and Gascoigne Halman – a gold member of Agents’ Mutual. When Gascoigne Halman signed up to Agents’ Mutual in January 2014, it was an independent and is now in the ownership of Connells, which bought Gascoigne Halman in October 2015.

The Competition Appeal Tribunal hearing, which is scheduled to last until February 20, is dealing with the competitive issues arising from counter-claims in response to cases brought by Agents’ Mutual against  Gascoigne Halman and another agent, Moginie James, as it seeks to enforce their contracts.

In the hearing, which opened on Friday, QCs for Gascoigne Halman and Agents’ Mutual advanced skeleton arguments. Moginie James is not a part of this procedure.

Appearing for Agents’ Mutual, Alan Maclean said the ‘one other portal’ rule had support, including initially from Gascoigne Halman.

He told the hearing that there was evidence of estate agents being fed up with the ‘duopoly’ of Zoopla and Rightmove.

Mr Maclean said evidence would be shown during the hearing on why the ‘one other portal’ rule was crucial to entry.

He said it was “essential that the launch of the portal disrupts the market”.

Suggesting that there might have been total exclusivity, he added: “The ideal way to do this is to get agents to do it exclusively. However the directors did not consider a requirement would be viable.”

Mr Maclean said that Primelocation – which is now part of ZPG – and Rightmove first had exclusivity agreements when they launched.

Appearing for Gascoigne Halman, Paul Harris QC was first to address the tribunal, and spoke about Agents’ Mutual’s business plan.

He said that this had forecast that Zoopla would lose 5,000 offices by 2015 and a further 2,000 in 2016, while Rightmove would not lose any in the first year.

Mr Harris alleged that the objective was to create a tipping point against Zoopla, which would “wither away and die” before going on to “undermine” Rightmove.

But Mr Maclean said these were “stylised” numbers. He said there was nothing wrong with being number three and working towards number two.

Mr Harris said: “Far from being a pro-competitive market entry story, this is a defensive, protectionist, anti-competitive story.”

Mr Harris also alleged that Agents’ Mutual had wanted to know the collective decisions of agents joining OnTheMarket and being informed of the other portal being used.

He said: “The contracts (with agents) are the fruits of this illegal concerted practice.”

The hearing continues.

Agents and Agents’ Mutual square up to each other in High Court