The concern relates to the fund’s acquisition of developer John Laing, which the complainants say contravened the fund’s stated intention to invest in low-risk assets with inflation proofing.
According to the action group, around two-thirds of the fund’s value was wiped out by the acquisition.
Henderson has consistently denied the fund did anything wrong.
“We have considered these complaints carefully,” the organisation said. “We are confident we have no legal liability to investors in this fund. We will vigorously defend these proceedings.”