In a bid to increase sales of mortgages through brokers, National Australia Bank will rebrand its broker-only product range and change its commission structure.NAB is underweight in the broker channel, with 29 per cent of its mortgage balances originated through brokers, compared with the industry average of around 40 per cent.During the six months to March, 34 per cent of NAB's mortgage flows came through brokers, compared with 38 per cent for Commonwealth Bank, 44 per cent for Westpac and 47 per cent for ANZ.To turn this around the bank will change its commission structure so that brokers will be paid a trail commission in the first year of the loan. At the moment trail commissions do not start until year two.NAB pays an upfront commission of around 60 basis points and a trail of 10 to 15 bps (NAB does not offer volume-based incentives).NAB is also re-branding its broker-only mortgage products. As reported in Banking Day yesterday, Homeside HomePlus and Homeside Peak Performance will be branded NAB HomePlus and NAB Peak Performance from August 18.And borrowers whose loans were originated by brokers will be able to use the bank for customer service (previously, they had to deal with their broker).NAB group executive for personal banking, Gavin Slater, said the bank was keen to continue increasing market share in home lending and saw the broker channel as a strong growth channel.Slater said NAB's broker originated mortgage book was growing at twice system, while the branch originated book was growing at system and business bank originated mortgages were growing below system.He said NAB had some advantages in the broker market that it was keen to exploit. It owns three aggregator businesses - Plan, Fast and Choice.It has a business that sells "white label" mortgage products to its own aggregators and the wider aggregator market.Slater said 12 per cent of mortgage flows were through white label products and he believed there was an opportunity to increase that share.He said the bank was working on its service levels to facilitate approvals and improve turnaround times.One reason for the emphasis on the broker market is that Slater believes that broker share will grow. "We see broker share growing to 50 per cent before it tops out," he said.