Jan 23 (Reuters) - Struggling music investor Hipgnosis Songs Fund said on Tuesday its investment adviser, which is backed by private equity firm Blackstone, had refused to drop the 'call option' from their advisory agreement.

Hipgnosis Songs Management, which is responsible for managing more than 150 song catalogues, holds a 'call option' that gives it the right to purchase the fund's portfolio if and when its agreement with the fund is terminated.

The London-listed fund had requested the investment adviser remove the option "to act in the best interests of shareholders as a whole".

It previously said that the option was a "structural conflict between the interests of our shareholders and the investment adviser" and also deterred potential bidders for the company.

HSF is calling an extraordinary general meeting on Feb. 7 to vote on a proposal to enshrine the payment of a fee of up to 20 million pounds ($25.5 million), as a form of "cost protection" to prospective offerors who may be deterred by the call option. ($1 = 0.7848 pounds) (Reporting by Yadarisa Shabong in Bengaluru; Editing by Savio D'Souza and Varun H K)