Heather McMahon

Call: 1999

Heather specialises in professional liability, insurance, commercial and regulatory work.

Heather’s main area of practice is professional liability claims and she has been ranked as a leading junior in this area by Legal 500 for several years. She acts for and against a wide range of professionals, with particular experience of claims against lawyers, surveyors, valuers, and financial professionals.

Heather also has substantial experience of professional indemnity insurance disputes, most recently in Discovery Land Company v Axis, a coverage dispute arising out of a former solicitor’s alleged fraud (with William Flenley KC).

Heather also has a busy commercial law and professional disciplinary practice. She appears regularly in the High Court, County Court and specialist tribunals.

Professional Liability

Heather has acted for claimants and defendants in claims involving all manner of professionals. She has particular experience of claims against lawyers, surveyors and valuers, and financial professionals. She is frequently instructed in large, document heavy cases which are particularly legally or factually complex.


Heather has extensive experience of claims against lawyers, arising out of most areas of legal practice. Her work includes claims arising from litigation gone wrong, including lost litigation and undersettlement claims, conveyancing and lender claims, claims arising from the conduct of family proceedings, including matrimonial finance disputes, and claims arising from non-contentious transactions, including contracts, wills and other property and trust disputes.

Her current and recent work in this area includes:  

  • a lost litigation claim arising out of failed employment tribunal and civil proceedings, said to be worth more than £3m;
  • acting for the solicitors in Jago v Mortgage4U and another, a claim for the lost opportunity to pursue mortgage brokers in respect of an interest only mortgage used to fund foreign property investment;
  • various substantial claims against solicitors arising out of allegedly inadequate advice given to purchasers in residential property developments; and
  • acting for the solicitors and former executors on a £20m contentious probate claim (with Francis Bacon).

Property Professionals

Heather is regularly instructed in claims against surveyors and valuers, typically arising out of alleged failures to detect or report on problems in residential property and alleged overvaluations. She has also acted in various claims against estate agents and property managers.

Financial Professionals

Heather has acted in a wide range of claims involving financial professionals, including accountants, IFAs, insurance brokers, insolvency practitioners and tax advisers.

Construction Professionals

Heather has experience of a number of claims against architects involving the provision of design and construction supervision services. She also has experience of claims against engineers of various different specialisms relating to residential property development.

Heather often acts in insurance disputes about insurance coverage, largely but not exclusively in relation to professional indemnity insurance. She has considerable experience of coverage disputes, particularly in relation to policy exclusions and aggregation issues.

She is currently instructed in Discovery Land Company v Axis, a coverage dispute arising out of a former solicitor’s alleged fraud (with William Flenley KC). She also recently acted in various arbitration proceedings relating to “after the event” legal expenses insurance policies.

Heather is regularly instructed to advise on a broad range of commercial matters, including contractual claims, claims arising out of fraud and deceit, business and property disputes, shareholder disputes, and claims for breach of trust and breach of fiduciary duty.

Her current and recent work includes several cases involving allegations of actual or suspected civil fraud, various recovery and enforcement claims, and claims for urgent relief, including acting for a Formula One engineer alleged to have taken confidential data belonging to his employer.

Heather has considerable experience of professional regulatory and disciplinary claims. She has represented registrants in healthcare regulatory proceedings for many years, typically in cases involving allegations of serious misconduct. Her work in this area includes the successful defence of allegations of misconduct and dishonesty regarding the condition of a baby at birth, which involved extensive expert medical evidence, and the successful defence of a registrant whose admitted medication errors were alleged to have contributed to the death of a patient.

"Heather is an exceptionally talented, client-friendly, very capable thorough. She is measured and calm, very organised and on her feet she is very impressive." Legal 500, 2024

"Very hard working, thorough, dedicated and intelligent." Legal 500, 2023

“She is super-sharp and thorough. A good communicator who works very hard.” Legal 500, 2022

“A very strong junior who works well in a team. She has an extraordinary ability to distil key relevant facts from vast amounts of material.” Legal 500, 2021

“Very good on complex matters”  Legal 500, 2020

Heather has a first class degree in law from University College, Oxford.  

Heather joined Chambers in 2009. Before joining Chambers, Heather worked as a judicial assistant to the then Vice-Chancellor, Sir Andrew Morritt. She then worked for the Government Legal Service for eight years, where she gained extensive experience in public and regulatory law.  

In 2004, Heather was awarded a Pegasus scholarship to work in Richmond, Virginia, USA, hosted by the John Marshall and Lewis F. Powell American Inns of Court.  

Professional Memberships 

Heather sits on the Executive Committee of the Professional Negligence Bar Association. She is also a member of the London Common Law & Commercial Bar Association.  

Publications and Lectures 

Heather assisted with research for Flenley and Leech, The Law of Solicitors’ Liabilities, fourth edition, 2020. Her own published work includes “Loss of a chance in commercial transactions”, Butterworths Journal of International Banking and Financial Law, 2021, 405 (with Michael Pooles KC). 

Heather regularly gives talks to clients in her areas of practice.  


Heather is an enthusiastic spectator of most sports and an occasional participant in a few. In her spare time, she enjoys cooking, travel and photography. 

ICO Data protection registration number: Z2003875. 

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