Hundreds of estate agents have expressed support for legal action against Rightmove, which is being accused of charging excessive and unfair subscription fees.
Shares in Rightmove were falling by about 5% after the case against the property website was filed with the Competition Appeal Tribunal.
It is being led by former panel member for the UK’s competition watchdog, Jeremy Newman, and seeking damages worth around £1.5 billion.
Mr Newman said there had been “an extremely encouraging response” from estate agents since the legal action was announced in November.
Around 250 businesses across the UK have expressed interest in and support for the claim, according to the group behind the case.
“Filing this claim today advances the route to meaningful compensation for those businesses who have had very little choice but to absorb excessive fee increases for many years,” Mr Newman said.
The claim alleges that Rightmove abused its dominant position in the UK online property portal market by charging thousands of estate agents and new home developers excessive and unfair subscription fees.
Rightmove responded to the claim being filed to say it is “confident in the value we provide to our partners and consumers” with a platform that supports “market transparency, liquidity and confidence”.
“As one of the most efficient parts of the UK housing market, we help people across the UK to move home by bringing buyers, sellers, renters, landlords and agents together,” it said.
“This claim is without merit and we will defend it vigorously.”
Based on the estimated total damages and size of the class action, it is understood that the claim assumes agents can be charged thousands of pounds in fees to use Rightmove.
Rightmove has previously come under scrutiny, with a petition gaining more than 2,000 signatures last year calling for an investigation into its pricing model.
The firm has been accused of squeezing small businesses and independent agencies with fees that are higher than what corporate chains pay.
The case is being funded by specialist litigation funder Innsworth Capital Limited with legal support from Scott+Scott UK.
Rightmove says it has the UK’s largest selection of properties for sale and to rent, with around 80% of all time spent on property portals being on its site.
The FTSE 100-listed firm made an operating profit of £288 million in 2025, up 12% on the previous year.
