A former junior solicitor struck off for lying to colleagues about leaving a briefcase on a train is appealing the decision, supported by a legal team acting pro bono.

Claire Matthews, who was struck off last month, last week filed her appeal at the Administrative Court on the grounds that the Solicitors Disciplinary Tribunal failed to investigate and properly weigh up the impact of the incident on her mental health. The appeal argues that the tribunal therefore erred in its findings of misconduct and dishonesty.

The SDT judgment relating to Matthews was updated yesterday to confirm that she intends to challenge the ruling in the High Court. The order to strike her off the roll remains in force pending the court’s decision.

Matthews said: ‘I feel it is important that this appeal is seen through so as to help highlight mental health in the legal profession and the devastating effect it can have when it impacts on careers.’

In her appeal Matthews will argue that the decision to strike her off was unduly harsh and excessive due in part to the tribunal failing to take into account factors including her good character, the fact that no harm occurred, that there was no gain to her financially or professionally and that it was a one-off incident. It is argued in her appeal that the tribunal erred in law by holding that the case did not fall under 'exceptional circumstances'.

The case attracted huge publicity when it emerged Matthews had been struck off for what she told her employer Capsticks after losing the briefcase, which contained sensitive documents. When asked where the briefcase was, she initially told her firm it was still at home, then after a week she said it had been lost but only that morning.

Matthews represented herself at the four-day tribunal hearing and told the panel she had been ‘overcome by uncontrollable fear, anxiety and panic’ in the days following her mistake. The tribunal heard evidence of a long-standing mental health condition that affected her ability to respond to what was happening.

The Gazette reported that lawyers had last week had offered to work pro bono on her case, leading to concerted efforts to trace her before the 21-day deadline for lodging an appeal. Matthews was inundated with offers from barristers and firms saying they wanted to help, while many lawyers also supported her cause through social media.

She is now represented in her case by the national firm Leigh Day and Mary O’Rourke QC and Rosalind Scott Bell of Deans Court Chambers.

Gideon Habel, head of Leigh Day’s regulatory and disciplinary team, said: ‘Claire feels very strongly that an injustice has been done and is determined to put that right. The case raises important issues, including about how we in the profession, regulators, tribunals and courts deal with mental ill-health in the legal profession.’

While the legal team is acting pro bono, Matthews is seeking funds in the event of an adverse costs order. A GoFundMe page has been opened. Any surplus will be donated to LawCare, which promotes good mental health and wellbeing for the legal profession.

It emerged in the tribunal ruling that Capsticks – the SRA’s regular legal adviser – had not reported Matthews' conduct, which had been flagged up by a person mentioned in the documents. The SRA said it has written to the firm reminding it of its obligations to promptly report possible misconduct. The firm has declined to comment.