Housebuilder Berkeley has reported a 20% slump in reservations for its properties, blaming higher stamp duty for landlords and Brexit uncertainty.
The firm said "the extraordinary attack on buy-to-let landlords" by the government had hit reservations.
However, its shares rose after it reported a 33.9% rise in profits to £392.7m in the half-year to 31 October.
The increase came as the company sold fewer homes at a higher price, selling 2,076 houses at an average of £655,000.
In April, the government introduced a 3% stamp duty surcharge for buy-to-let landlords and people buying second homes.
Some housebuilders have warned of a possible slowdown in construction due to greater uncertainty facing the UK economy in the wake of the Brexit vote.
Housebuilders who operate across much of the UK are still reporting increased demand, but sales have been hit in London, where a higher proportion of buyers are investors and many come from abroad.
Berkeley, which specialises in high-end property, urged government to bring clarity to Britain's Brexit terms.
"We put a plan forward to build our homes but if you create conditions that are so uncertain or you create a downturn, then that will really cause us to build less homes," said chief executive Rob Perrins.
The firm said reservations, when a buyer pays to take a home off the market, had been down 20% for several months.
However, a separate survey indicated that construction activity across the UK in November rose at its fastest rate since March.
The Markit/CIPS UK Construction Purchasing Managers' Index (PMI) edged up to 52.8 from 52.6 last month, helped by strong demand for residential projects. A figure above 50 indicates growth.
But the survey also indicated that costs faced by builders rose at the fastest pace since 2011. Markit said was mainly down to the recent weakening of the pound, which has pushed up the price of imports.