Recent research by the organisation found that the proportion of mortgages originated from the intermediary sector stood at 75 per cent in the first quarter of this year.
According to Mr Williams, the growth of the mortgage adviser has "changed everything" in the market.
"Consumers for their part have benefited greatly from the myriad of products available to them, and from the expert and independent advice provided by intermediaries who guide them through this bewildering market place," he added.
Recent research by the IMLA found that remortgaging and standard status business are increasingly dominating the mortgage market.
According to the body's survey of intermediaries, almost half of all mortgage cases were remortgages, with respondents also expecting an increase in the near future.
Click here to run an energy price comparison, and see if you could be paying less for your gas and electricity.