By comparison, around 11 per cent believe it will fall, with brokers on average expecting to do around 0.8 per cent more business this year.
It is the second quarter in a row in which advisers have forecast their buy-to-let business will grow over the coming 12 months.
The study also revealed a jump in the proportion of landlords taking out buy-to-let deals for portfolio extension had risen to its highest level in two years.
One in four buy-to-let deals were secured in the last quarter of 2019 for this reason, the highest figure since the first quarter of 2017, Paragon said.
Half of buy-to-let deals were remortgages, down from 55 per cent in the previous quarter. Almost two thirds of these remortgages were in order to secure a better rate of interest, with 31 per cent looking to raise funds.
Brokers said that buy-to-let accounted for around 17.7 per cent of their overall business during the last quarter of the year, the highest proportion in a year.
Richard Rowntree (pictured), managing director of mortgages at Paragon, said that while buy-to-let has been driven by remortgage business in recent years, it was encouraging to see the proportion of borrowing for extending portfolios hit its highest level in nearly three years.
He continued: “It’s also encouraging to see that the balance of brokers expecting to write more buy-to-let business is positive for 2020 as confidence has been subdued for much of the past four years. These are green shoots and we hope they will continue throughout this year on the back of a more certain regulatory, economic and political environment.”