ESG funds - which claim to promote environmental, social and corporate governance best practice - are all the rage. But are investors being taken for an expensive ride?Ed Butler speaks to one man with his doubts - Tariq Fancy, who used to be in charge of sustainability investing at BlackRock, the gigantic fund management firm, whose boss Larry Fink is an advocate for the role that big finance can play in accelerating the transition away from fossil fuels.Today investors are faced with a confusing menagerie of products that purport to be climate-friendly, as described by Dylan Tanner of the lobbying research firm InfluenceMap. In reality, many of them charge high fees for some pretty questionable environmental benefits. But if investors feel misled, could they find legal recourse in the form of a class action lawsuit? Ed asks Fiona Huntriss of the UK law firm Pallas Partners.Producer: Victoria Broadbent(Photo: $100 bill covered in green paint; Credit: Getty Images)