Mortgage aggregator AFG did almost 40 per cent of its business with investors in March. AFG said 39.6 per cent of mortgages processed last month were for investment property.The company said this was the highest level of investor participation it had recorded since it started reporting mortgage data seven years ago.In New South Wales investors accounted for 49 per cent of AFG's business and in Victoria the figure was 37 per cent.AFG brokers wrote A$4.05 billion of loans in March - an increase of 7.7 per cent over the previous month. The average loan size was $436,000 and the average loan-to-valuation ratio was 68 per cent.