Allen specialises in property, commercial, banking and administrative law. He is ranked in Band 2 by the Chambers Global Legal Directory and is noted for his impressive record in contentious mandates. He is a legal reformist, participated in drafting of Kenya’s Court Mandated Mediation Rules, Advocates Remuneration Orders 2006 and 2014 and was involved in drafting practice directions for various divisions of the High Court and the Court of Appeal. As President of the LSK, he within 100 days launched an office manual, a mentorship program for young lawyers and a bar-bench practice guideline. He is a Chartered Arbitrator and former Director of Nairobi Centre for International Arbitration.
Allen reduced his experience and knowledge in his book Litigation- The Art of Strategy and Practice, Nairobi: 2017, Law Africa Publishing Ltd. He is an adjunct lecturer at the Kenya School of Law where he lectures on the practice of litigation. Allen mentors young advocates and freely advises colleagues on litigation.