A further 15% believe the market could reach over £260bn.
The club surveyed the broker audience at its Mortgage Club Live Conference in London this month on a raft of issues.
In response to questions posed by chair and mortgage club director Jeremy Duncombe, 51% also believe an interest rate rise would increase business.
Legal and General said the results clearly show the potential brokers see for a rise in new business enquiries after a near-term rate rise, as consumers looked to secure favourable rates with a fixed term mortgage ahead of any further increase by the Bank of England.
“It also highlights the need for brokers to get in touch with any clients approaching the end of their mortgage term now, to help them get the best deal before the central bank raises rates for the first time in a decade,” said the club.
However, over a third of brokers expect a rise to have no impact on their business, and a smaller number believe a rise would decrease their business activity over the next year.
Jeremy Duncombe, director of Legal & General Mortgage Club, said: “The mood remains positive among brokers. This positivity is a reflection of a market that remains robust in the face of Brexit uncertainty and in which the choices for borrowers continue to grow. New lenders, increased competition, good availability of funding and higher loans-to-value mean lenders are still very willing to lend and most brokers expect to see this continue into 2018.”