Berkhamsted in Hertfordshire came in second place, with a surge of 58% in sales being agreed, and a drop of 57% in new sellers. Witney in Oxfordshire takes the third spot with sales up 51% and new sellers down 59%.
Newmarket in Suffolk has shown the biggest gap over the past year between the number of homes selling and new sellers bringing their properties to market, according to Rightmove.
The number of sales being agreed in the town was up by 79% year-on-year in July, while the number of new sellers putting their properties up for sale was found to be down by 49%.
Berkhamsted in Hertfordshire was second on the list, with a surge of 58% in sales being agreed, and a drop of 57% in new sellers.
Witney in Oxfordshire saw sales rise by 51%, while the number of new properties being brought to market was down by 59%.
The top 10 new supply shortage hotspots were all found to be in the South East and East of England, with average asking prices in three of the hotspots - Newmarket, Berkhamsted and Bushey - up by 9% since 2019.
Nationally, the average number of available properties on an agent’s books was 16 in July 2021, down from 29 in July 2020.
Tim Bannister, director of property data at Rightmove, said: “If we think back to July last year the market in England had been open again for around six weeks, the stamp duty holiday was announced, and a summer frenzy was just beginning.
"12 months on, the combination of fewer sellers coming to market and sustained demand has resulted in a summer seller shortfall, and so the challenge for agents now is to try and replenish the stock to meet the demand from buyers.
"For those considering coming to market this year, now could be the time to find out what your home could be worth from a local agent.”