Mining giant Anglo American has rejected BHP Group’s £31.1bn proposal after it concluded the plan would undervalue its future prospects. The talk of a potential mega-deal between BHP and London-listed miner Anglo American had the mining world’s attention this week, and it seems to have attracted the attention of activist investor Elliott Investment Management. Bloomberg has reported that the hedge fund, known for its activist campaigns, has acquired a $1bn (£800m) stake in the miner. The news…