One of National Australia Bank's fastest growing businesses is its wholesale loan servicer Advantedge. NAB reported at yesterday's June quarter update that Advantedge's loan portfolio had grown 12 per cent in the quarter to $5.5 billion.Advantedge works with about 4000 brokers who are aligned with one of the company's three aggregators, Plan, Fast and Choice. It also works with a number of mortgage managers. NAB bought the business, then called Challenger Mortgage Management, from Challenger Financial Services last year.It was a well timed acquisition. Industry consolidation, the National Credit Act and a lack of alternative funding sources have been good for groups like Advantedge.With a move to bigger, better resourced and more tightly regulated brokers and mortgage managers, Advantedge is changing the way its works with its "customers". It is expanding the range of mortgage managers who operate with a delegated underwriting authority.Last week Resi Home loans announced that it had a delegated underwriting authority for loans serviced by Advantedge.Advantedge chief executive Drew Hall said: "It is a powerful tool for our customers. They can provide a more direct service to their clients."For us there is a scale benefit. It effectively widens our workforce."We don't give carte blanche. There are parameters around loan size, LVR, serviceability, security type and location. And we only give the authority to organisations that are well resourced and have reputable brands."Because these organisations have skin in the game you can find their control processes are more powerful than our internal underwriting."Delegated underwriting has been around for some time but the new licensing regime is a pathway that will mean more mortgage managers have the scale and resources to do this. There is scope to expand this side of our business."