By Elliot Gulliver-Needham The board of Hipgnosis has said it would recommend a bid from private equity giant Blackstone to its shareholders if the company makes a firm offer. On Saturday, Blackstone revealed it had kicked off a bidding war for the music-focused investment trust by making a rival offer to the one put by Concord Music. Concord had valued Hipgnosis Song Fund at $1.4bn (£1.1bn) in its bid last week, but Blackstone floated an offer seven per cent higher. Blackstone is the majority owner of the trust’s investment adviser Hipgnosis Song Management (HSM), and had made four offers beh…