Leslie Allen was called to the Bar in 1983. After practising at the Bar, he worked in the legal departments of the London Borough of Sutton and Westminster City Council before joining the Government Legal Service and HM Customs and Excise from 1987 until 1991. It was here that he was first involved in tax disputes, representing the government in this area. From 1991 until 2002, he worked at KPMG, and then Ernst & Young. This time, he represented taxpayers against what is now known as HM Revenue and Customs (HMRC).

From 2002 until 2023, he was a partner at Dorsey & Whitney LLP, DLA Piper LLP and Mishcon de Reya LLP. He recently formed his own tax dispute business, Allens’ Tax Disputes Ltd.

Leslie has some 36 years’ experience in tax disputes, ranging from tax fraud cases, VAT disputes, HMRC disputes, Code of Practice 8 and 9 disclosures, through to National Minimum Wage and IR35 disputes. Today, he handles many disputes using alternative dispute resolution. He has remained active as an advocate in the courts, and successfully represented GE in one of the last ever UK CJEU referrals.

He has been involved in many leading cases over the years, including cases involving the Zoological Society of London and Mercedes Benz Financial Services Ltd at the CJEU.