Property is a national obsession and 80 per cent of the searches for homes to buy, to rent – or to merely dream of – are carried out on Rightmove.

Yet powerful hedge funds appear to believe the property portal’s dominance may be under threat from rival Onthemarket which is receiving huge investment from CoStar, its US owner.

Investment partnerships have made record bets against the firm via short-selling deals in which traders borrow shares and offload them. 

The hope is the share price will fall substantially before the trader must buy them back to restore them to their owner with a fee. Almost 3.5 per cent of Rightmove’s shares, worth £150million, are out on loan.

Rightmove is the go-to for those seeking a home, with traffic set to increase under the Government’s policies to boost house building and make home ownership easier for first-time buyers.

CoStar’s chief executive Andy Florance has previously lashed out at Rightmove, saying that the portal which was established at the height of the dot-com boom in 2000, had ‘grown complacent’.

Sean Kealy, equity analyst at Panmure Gordon, said: ‘The fear is either that Rightmove’s growth will slow, or its margins decline as CoStar attempts to muscle in.’

In the industry, Rightmove is felt to benefit from a very powerful and established ‘network effect’: the more properties listed on the site, the more househunters and tenants seeking a rental home it attracts. This is extremely hard to replicate or disrupt.

Rightmove makes money by charging estate agents to show their properties on its platform.

At its recent Investor Day, the property portal said it is set for expansion. It expects revenues of more than £600million by 2028 which would more than double its current size.

Rightmove declined to comment. Onthemarket was contacted for comment.