Zoopla has sailed back into the attack on OnTheMarket, saying that the new portal is seen by sellers and home hunters as unimportant.

It says that agents are largely chosen on the basis of which portals they advertise on, and warns that some could be trying to win instructions “with one arm tied behind their back”.

OnTheMarket has, however, revealed that Tuesday this week was its best ever day for traffic and that last week it delivered the most leads to agents in its less-than-five months history.

According to a new survey conducted by Zoopla of over 4,000 home owners, 89% would expect their properties to be advertised on Rightmove and 88% on Zoopla.

When asked which single website they viewed as most important to be on as part of the agent instruction process, 47% chose Rightmove, 47% chose Zoopla, and just 2% chose OnTheMarket.

Zoopla, which conducted the survey among those registered with it between June 11 and 15, also asked respondents where they looked for property.

Over 90% said they searched primarily through property websites, with 48% saying if they could use only one site it would be Rightmove, 46% opting for Zoopla and less than 1% choosing OnTheMarket.

According to the survey, 91.6% believe that where their agent markets their property is either important or extremely important, 94.2% expect their agent to automatically maximise the marketing exposure of their property and 91.5% would consider switching agents if they found out that was not the case, with a further 6% stating they would look to renegotiate fees as opposed to switching.

By far the largest proportion of respondents (41.5%) stated that the property websites the agent advertises on is the single most important factor in choosing which estate or letting agent to instruct.

In comparison, 21% and 15% stated that fees and valuation respectively were most important and just 2% who said that local newspaper exposure mattered most.

Lawrence Hall of ZPG said: “This latest data shows clearly that home owners expect their properties to be marketed as widely as possible and that agents who choose not to are operating with one arm tied behind their back when trying to win instructions.

“It also shows just how far local print has fallen and property websites have risen in terms of importance with sellers in a relatively short period of time.”

OTM chief executive Ian Springett said: “OTM launched just over four months ago and is continuing to grow in both size and momentum.

“On Tuesday, OTM enjoyed its best ever day for traffic and last week it recorded a record number of leads for our member agents.

“Meanwhile, our highly effective marketing campaign will continue across TV, press and online for the coming months to ensure awareness for the brand continues to increase.

“Last month, Zoopla revealed it had lost 23% of agents between March 2014 and March 2015.

“Less than 10% of our current members have retained Zoopla as their one other portal, so it is clear that Zoopla is losing market share to both OTM and to Rightmove.”

While Rightmove is mentioned in Zoopla’s latest press release, it says it knew nothing about it.

Its own latest statistics show that it received double the number of visits than any other property website, recording 115m visits in its busiest May.

* Rightmove’s staff conference is taking place today and tomorrow. A spokesperson said: “The customer service team will still be answering urgent email enquiries and phone calls from our customers throughout the two days.”