Iain MacWhannell

Contentious Tax, Commercial & Chancery Litigation, Investigations

Before pupillage, Iain worked for HMRC Solicitor’s Office in both Excise and VAT. He has acted as counsel both for and against HMRC in a variety of disputes in the Tax Tribunal, Upper Tax Tribunal, High Court (Admin, ChD and Comm), Court of Appeal (Civil), House of Lords and UK Supreme Court. He became a partner at JHA in 2021 and prior to that had been a tenant at a leading set of Chambers and a Dispute Resolution Partner at a City law firm.

Bar of England & Wales

Iain was called to the Bar in 2006 and his practice focuses on contentious tax. He has litigated several of the leading cases on HMRC’s investigative powers, tax fraud, evasion/avoidance, and tax abuse. He continues to have a market leading presence in these areas.

Iain manages a wide variety of work for an international client base, ranging from PLCs to UHNWs and owner-managed businesses to trusts and funds. He is often sought out by other professional advisors for a second opinion and to help ‘unlock’ long-running or complex problems.

Iain began his career at HMRC Solicitor’s Office (Excise and then VAT litigation). At the Bar, and in private practice, he has acted as counsel both for and against HMRC in the Tax Tribunal, Upper Tax Tribunal, High Court, Court of Appeal, House of Lords and UK Supreme Court. He became a partner at JHA in 2021 and prior to that had been a tenant at a leading set of Chambers and a Dispute Resolution Partner at a City law firm.

Iain has successfully litigated multiple legally-significant and high-value tax disputes in the last 12 months, including:

(1) In January 2024, he acted for over 24,000 companies in the largest ever Tax Tribunal group litigation. The case concerned the VAT de-registration of thousands of companies and involved allegations of fraud and abuse.

(2) In November 2023, he acted as part of the team in the Franked Investment Income Group Litigation.

(3) In October 2023, he successfully discharged HMRC’s case on day 3 of a 10-day trial. These cases were the first of their kind in the new wave of disputes with HMRC regarding the application of the Kittel (fraud) and Fini (abuse) principles in the Tax Tribunal.

Iain has managed concurrent tax investigations and specialist tax proceedings across multiple European jurisdictions.