Buy-to-let mortgage sales surged by 163% in the year to March as landlords raced to beat the new stamp duty surcharge on 1 April.
Landlords borrowed £7.1 billion in March, up 87% month-on-month and 163% year-on-year.
Loans totalled 45,000, a rise of 88% on February and 142% compared to March last year.
First-time buyer activity also increased, with the £4.5 billion borrowed up 32% on February and 29% on March 2015 year.
Paul Smee, director general of the CML, which produced the figures, said activity was distorted by the rush to beat the 3% stamp duty surcharge.
"These supercharged levels of activity are likely to be temporary and will fall back over the summer months.”
Mark Harris, chief executive of mortgage broker SPF Private Clients, said: “Many landlords brought forward decisions to buy, with the market now likely to pause for breath as investors consider their next move, possibly later in the year."
Harris didn't expect to see a significant slowdown in residential mortgage activity. “There are still excellent mortgage rates available, both fixed and variable.
“Interest rates are unlikely to rise anytime soon which will continue to attract first-time buyers and second steppers to the market.”
David Whittaker, managing director of Mortgages for Business, said March was an “electric” month for buy-to-let with "practically unheard of" growth.
“For many landlords thousands of pounds were at stake, injecting the market with considerable dynamism.
He said the dust will begin to settle on buy-to-let through the second quarter of the year. “Landlords' investment strategies will also have to take into account upcoming tax relief restrictions plus increased income cover ratios from many lenders.”
David Catt, chief operating officer at Hometrack, said: “Attention now turns to the impending EU Referendum. Homeowners will take a more cautious approach to purchasing decisions and will favour knowing the outcome of the Brexit vote before increasing their borrowing.”