Spencer has held stakes in numerous public and private companies. He is a director and majority shareholder in IPGL, a private holding company making investments on behalf of Spencer and other family trusts. He is also an early-stage investor in Temple Grange Partners, a consultancy that finds compliance specialists for financial markets, and an investor in mobile gaming software company Probability. He is a co-owner of Exotix, a frontier markets investment banking boutique. He also owns a stake in Cluff Natural Resources, an energy resources investor. In 2018 he led an investment round in two cyber security firms: Veridium, a biometric authentication startup, and Glasswall Solutions, a file regeneration technology firm.