Haart is urging the Chancellor to relax the buy-to-let taxation crackdown after its data showed the number of landlord registrations was down by more than a third during January.
The agent’s data showed the number of landlords registering to buy rose by 2% between December and January, but fell 37.4% annually.
In London, the number of landlord registrations was down 41.3% annually.
Its branches did, however, report that the number of national sales to landlords was up 13.9% annually in January.
In sales generally, branches reported a 15.2% annual boost in new listings, a 2.6% rise in buyer registrations and a 5.5% yearly increase in exchanges.
Paul Smith, chief executive of haart, said: “There is a clear appetite to move amongst buyers and sellers.
“Just one month from Brexit, buyers are continuing to act in ignorant bliss, ignoring formidable predictions that are still dominating headlines.
“With increased confidence in activity, we can expect price rises over the coming months.
“But January was very much a tale of two halves. The London market did not pick up in the same way that the rest of the UK did, and the number of new instructions for sale in the capital dropped by 2.6%.
“The lack of new homes to buy has, in turn, pushed up rental prices by 6% on the year to a record £1,924 as Londoners scramble for rental accommodation as an alternative to buying a home.
“This is a not a fault of Brexit, but rather a consequence of the Government’s misguided efforts to reform the property market with taxation on buy-to-let landlords.
“Until buy-to-let taxation is relaxed, we can expect rents to rise throughout 2019 and tenants will increasingly be faced with difficulty when finding a new home in the capital.”