Mortgage aggregator AFG has reported a big increase in the number of fixed rate loans being written by its brokers.Fixed rate lending made up 17.7 per cent of total lending by AFG brokers during the March quarter, compared with 14.3 per cent in the December quarter and 11.4 per cent in the September quarter.AFG general manager sales and operations, Mark Hewitt, said borrowers were taking advantage of low fixed rates."With rates at historical lows the downside risk of fixing is relatively small, so many borrowers are choosing to lock in now," Hewitt said."And there are no guarantees lenders won't make their own moves outside the Reserve Bank cycle. Some are talking about increased funding and regulatory costs."AFG also reported a pick-up in investor activity. Investors made up 33 per cent of AFG's business during the March quarter - up from 31 per cent in the December quarter.Investor activity peaked at 40 per cent of AFG's business in the middle of last year.