35 WOMEN UNDER 35 2016: Sarah Keegan, 30 

Beginning as marketing intern at OVO Energy in 2009, Keegan, now head of brand, has nurtured the quirky, cuddly brand identity which has helped the company to become that great rarity, an energy firm whose customers actually like it. Her first year’s marketing budget was £10,000; today it stands at £11m. OVO’s turnover in 2016 is expected to be £750m.