Members of the Finance & Leasing Association (FLA) wrote £89 million worth of new second charge business in September.
This figure was 11% more than for the same period last year.
The number of new agreements totalled 1,958, also 11% up year-on-year.
Fiona Hoyle, head of Consumer and Mortgage Finance at the Finance & Leasing Association, said: “In September, the second charge mortgage market reported its strongest rate of new business volumes growth since January.
“New business volumes have grown by 4% so far in 2018, in line with expectations of single-digit growth in 2018 overall.”