Yet they have accounted for a growing share of investment in commercial real estate in Britain in recent years. According to a recent Bank of England report, these funds have about $46 billion in assets under management, representing 7 percent of investment in the British market." http://www.nytimes.com/2016/07/07/business/dealbook/3-more-p... the linked article.
So it seems this is maybe 3 percent of the overall British mutual fund market, and a fairly exotic part.