The property comparison website’s June house price index showed the price of property coming to market reached all-time high, up 3.0% (+£8,460) to £294,351.
The firm said election certainty boosted buyer activity but added that the anticipated rise in new seller numbers had failed to materialise.
The site saw 115 million visits in May - its busiest ever May – equal to every adult in the UK visiting twice in the month.
It also revealed tighter supply with the number of properties coming to market down 8.5% on same period a year ago, though £2m plus properties bucked this trend with 86% month-on-month leap in new listings.
Jonathan Hopper, managing director of the buying agents Garrington Property Finders, said: "Such a big jump in asking prices should not be dismissed as a mere post-election relief rally.
"Both sellers and buyers have been energised by the abrupt end to the pre-election uncertainty, but sellers are being buoyed too by the knowledge that demand still outstrips supply.
"With asking prices now at record levels in six of the 10 regions covered by the Rightmove index, some sellers risk crossing from bullishness into bravado.
"Buyers may be fighting for the very best properties, but they remain sensitive to both price and affordability.
"Overconfident vendors may feel it's a sellers' market, but buyers are not repeating the mistakes of the last boom.
"For all their determination to buy, most are being very discerning too."
