Rightmove says fewer new sellers are coming to market, with this month's total some 5.3 per cent below the monthly average for this time of year since 2010.
It says the biggest reluctance is coming from owners of larger homes with four or more bedrooms, with 6.6 per cent fewer sellers.
Given the well-documented structural shortages of housing supply any longer-term reluctance of owners to come to market would be a worrying trend, the portal warns in its latest house price report.
"If you're debating whether to trade up and make a big financial commitment you naturally might hesitate before putting your property on the market just a few weeks before you know the vote outcome" says Rightmove director and market analyst Miles Shipside.
"The number of new listings is still about 95% of the norm for this time of year, so the drop-off is relatively small in spite of what many are calling the biggest vote of our generation. This could mean that people are struggling to assess what the impacts might be, or are choosing to ignore them until they become more apparent" he says.
"A vote to Remain should mean that the housing market quickly returns to its previous norm, but a vote to Leave would create political and economic uncertainty, which historically has had more serious repercussions" Shipside warns.
However, the portal's price index out this morning nonetheless shows a new high for the average price of property that is coming to market - £310,471 following a monthly rise of 0.8 per cent.
There have been price rises every month so far in 2016, showing that the uncertainty associated with the EU referendum has failed to halt this year's upwards price momentum - in contrast to the run-up to the May 2015 general election, when the electoral uncertainty resulted in a price fall of 0.1 per cent in the month of the election.
Rightmove says the first quarter buy to let surge ahead of the stamp duty surcharge deadline has exacerbated the shortage of suitable property for sale; the result is that the average time it takes to sell a property is at its lowest level since Rightmove started monitoring it in 2010.
The average number of days to sell stands at 57 this month, down from 60 the previous month. At this time last year it was 65 days.
Rightmove says that while some prospective buyers are putting in offers within hours or days, this is an average for all properties and the timescale is from when a property is first marketed on Rightmove to when the estate agent marks it as "sold subject to contract".
"With today's tighter lending criteria, marking a property as sold before you're certain that the buyer has the means to pay for it could mean missing out on other more suitable purchasers. It takes time to check that a prospective buyer can get a mortgage, and ensure that all other buyers in the chain are also in a position to proceed. In spite of these extra delays and necessary diligence, the length of time to sell is the lowest we've ever measured" explains Shipside.
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