City, a 7 per cent shareholder in the commodities giant, said it was especially disappointed given the strong performance of the BlackRock trust over the medium-term.
Performance of fund vs benchmark over 3-yrs
Source: FE Analytics
"[The trust’s] investment returns over the three years to the end of October 2011 have exceeded 150 per cent. This is very satisfactory compared to the benchmark HSBC Global Mining Index return over the same period of 128 per cent," said City of London IG in a letter.
"However, we are disappointed that this good investment record is not more fully reflected in the share price, which remains at an unreasonably large discount to NAV. This is clearly an area where the board needs to be more assertive."
The authors said they had written to the BlackRock trust concerning this issue in April 2010 and in June 2011, and they consider the time for action is long overdue.
The £1.09bn BlackRock World Mining trust is run by Evy Hambro and is trading at a discount of 16.2 per cent, according to FE Trustnet data.