In its first results delivered to the City since the launch of OnTheMarket, Zoopla said it had lost 23% of its UK agency members as at March 31.

OnTheMarket, with its “one other portal” rule had launched two months previously.

Zoopla said it went on to lose another 106 agents in April.

As at March 31, there were 12,449 member agents, down from 16,261 the previous year.

Zoopla’s total membership – which includes developers, overseas agents and commercial firms – stood at 16,076, down from 19,239 the previous year.

However, Zoopla insisted that “churn levels have slowed significantly over the past few months and are returning towards normal historic levels”.

It made more money from its member agents (ARPA), £353 in the six months to the end of March compared with £311 the previous year, a rise of 13%.

For the six months to the end of March, Zoopla announced record revenues, up 10% to £42m.

It made an operating profit of £18.2m, up 12% from the year before (£16.2m).

It also announced traffic up 11%, with an average of 44.2m monthly visits.

Zoopla also highlighted its proposed acquisition of uSwitch for £160m plus a performance-based earn out of up to £30m.

CEO Alex Chesterman said: “We had a strong first half with both revenues and profits seeing double-digit increases and ARPA at record levels despite the reduction in members during the period.

“Our audience continued to grow with average monthly visits during the first half at 44.2m and mobile devices accounting for over 60% of these, up 34% year-on-year.”

City analyst William Packer of Exane BNP Paribas said that it expected membership churn in May to “still be negative”.

He went on: “Additionally, traffic data is tepid. Visits +11% vs H1 14 but down -3% vs H2 14, the first half on half fall since the group started releasing numbers, although Zoopla argue seasonality makes comparison more difficult. We expect market share loss to Rightmove.

“We expect a broadly neutral reaction on the in-line numbers and comments from management on churn returning to normal in the ‘coming months’. We remain cautious. We note that consensus expects a sharp positive rebound in agency membership by end of 2015 and 2016 which we see as unlikely.”