Foxtons has said sales rose by a record 16.2% to £38.4 million in the first quarter after buy-to-let investors rushed to beat the rise in stamp duty that came into force in April.
However, the London estate agent also warned that Brexit fears could result in a challenging six months.
"We expect the first half of the year to be challenging with a reduced sales pipeline entering into Q2 and the underlying short-term impact on transaction volumes from the uncertainty around the European referendum," chief executive Nic Budden said.
Foxtons saw commissions from property sales rocket 28.5%.
Mr Budden added: "We have had a strong start to the year with a record first quarter driven by a number of sales transactions being brought forward before the introduction of the additional stamp duty surcharge on buy-to-let properties.
"Our expansion strategy remains on track as we continue to increase our market share in outer London."