O John realiza toda a gama de trabalhos importantes de litígio e advocacia, incluindo a localização de activos, litígios multijurisdicionais e litígios comerciais e fiduciários. John tem sido advogado em muitos dos principais casos de litígio perante o Tribunal Real de Guernsey e o Tribunal de Recurso de Guernsey e é um dos poucos advogados de Guernsey a ter aparecido como advogado no Conselho Privado. Nos últimos 12 meses, foi o advogado principal em casos inovadores de litígios relativos a fundos fiduciários.

John was a founder member of ICC FraudNet, and is a member of the UK Fraud Advisory Panel. He was also a founder member of the Guernsey Royal Court Working Party which completely reviewed the island's Civil Procedure in 2008. He is also a member of the Association of Contentious Trust and Probate Specialists and is a Notary Public. John was the first elected Head of the Guernsey Bar in novembro 2008 and was re-elected to the role in 2010. In 2014 John was awarded ACTAPS Offshore Contentious Lawyer of the Year Award. In 2015 he was awarded the "most highly regarded" classification for Asset Recovery by Who's Who Legal – one of only five offshore lawyers in the world to be awarded such accreditation.