Assets peaked at £200.3bn on 31 July, reaching a new record.
They have doubled in the last six and a half years, having reached £100bn at the end of January 2013.
Close to half of the growth over that period (46%) has come from investment companies investing in alternative assets, which had £80.3bn under management on 31 July, up from £34.7bn on 31 January 2013 (growth of 132%).
Ian Sayers, chief executive of the Association of Investment Companies (AIC), said: “It’s good news that the investment company industry is growing strongly, reaching a record £200bn of assets at the end of July.
“This growth demonstrates the adaptability of investment companies, which have been helping investors meet their financial needs for more than 150 years.
“It reflects growth in mainstream investment companies which are investing in cutting-edge opportunities such as technology, healthcare, frontier markets and venture capital.
“As investment companies are the natural home for illiquid assets, it is not surprising that a significant part of this growth has been in the alternative sectors, which are often invested in assets that are harder to sell such as property and infrastructure.
“Investment companies’ income advantages have also come to the fore in the current low interest rate environment. Many investment companies have increased their dividends for decades, making them highly sought after in recent years.”