High street lenders have tightened criteria for self-employed applicants, the survey suggested.
The poll also showed that more than eight in 10 brokers believe client income has generally become more complex over the last 12 months.
Advisers indicated that many lenders had struggled to “take a view” on self-employed clients who had used a legitimate government grant.
The key factors differentiating “mainstream” from “specialist” cases are around income, credit history, credit score, loan size and property type, according to the study.
A third of brokers questioned said that more than half of their cases from the previous 12 months could be described as “specialist” whilst a further quarter said up to half of their cases had been “specialist”.
Almost eight in 10 brokers believe the specialist mortgage market represents a bigger opportunity today than in the past.
Buster Tolfree, director of mortgages at United Trust Bank, said: “Many applicants no longer fit traditional ‘tick-box’ criteria and that group is only going to get bigger.
“The way people earn their income or incomes has and will continue to change. As such, income criteria will be an increasingly important factor for brokers when choosing where to place their cases.
“Although many applications will require the skills and judgement of an experienced professional to properly assess suitability, that same knowledge and flexibility can be applied when designing and managing auto-underwriting systems and criteria.”
