Overall support for OnTheMarket has reached in excess of 6,500 UK estate and letting agent offices.

The figure represents an increase of more than 50% since this time last year.

The figure consists of contracted members and agents who have signed a Letter of Intent to join OTM when total support reaches 7,500 offices.

Today’s announcement comes just eight weeks after OTM revealed that support had exceeded 6,000 offices.

The site said that its “tried and tested use” of using non-binding Letters of Intent has been its primary method of building membership of the portal.

It said that previous versions of the letter in 2013 and 2014 were “very strong drivers of substantial growth in membership numbers”.

It added: “OTM gathered its initial 1,800 Gold member offices in 2013 with this approach and contributed to attracting over 2,800 Silver and Gold member offices in 2014. The rate of conversion to contract in both cases exceeded 80%.

“The latest Letter of Intent programme started at the end of June 2015 and sign-up by agents is now growing in momentum across the country.

“As with earlier phases, the Letter of Intent scheme runs alongside the recruitment of fully contracted members.”

OTM this morning confirmed that its next major milestone is to reach the overall support of at least 7,500 offices.

Ian Springett, chief executive of OTM, said: “This latest announcement which reveals the support of more than 6,500 offices is an indication of how the momentum behind the portal is building across the country.

“We look forward to welcoming to the only agent-owned, agent-controlled portal more and more agents who seek to regain strategic control of their data and costs.

“The more agents who join OnTheMarket.com, and the sooner they do so, the more powerful the portal will become in continuing to disrupt the duopoly and in providing a first-class alternative search service for consumers and agents alike.”

City analyst William Packer of Exane BNP Paribas was swift to comment.

He said that the figure of 6,500 compares with ‘well over 6,000’ reported in November.

He went on: “This is solid momentum and re-emphasises the risks to Zoopla of another tranche of members leaving.”