The governing statute is the Employment Rights Act 1996. Underperformance dismissals run through section 98, which sets a two-stage test: first the employer must show a potentially fair reason, here capability under section 98(2)(a); then the tribunal asks whether the employer acted reasonably in treating that reason as sufficient, applying the range of reasonable responses standard under section 98(4). A genuine performance concern is not enough on its own. Procedure carries equal weight, and a sound reason can still produce an unfair dismissal if the process was rushed, opaque or unsupported.
The procedural benchmark is the ACAS Code of Practice on Disciplinary and Grievance Procedures. Failure to follow it does not make a dismissal automatically unfair, but a tribunal must take it into account and can uplift compensation by up to 25% where an employer has unreasonably failed to comply. ACAS guidance is explicit that a fair capability process requires adequate support, meaning training, coaching or workload adjustment, plus a genuinely reasonable improvement period measured against the seniority and complexity of the role. A three-week plan for a complex senior post rarely survives scrutiny.
Two further points shape current practice. The employee has a statutory right to be accompanied at any formal capability meeting by a colleague or trade union representative under section 10 Employment Relations Act 1999. And the Employment Rights Act 2025, which received Royal Assent in December 2025, will reduce the qualifying period for ordinary unfair dismissal from two years to six months, with commencement set for 1 January 2027 and the statutory compensation cap removed at the same point. The practical effect is that performance management during the early months of employment is becoming materially higher-risk, so the discipline of a documented PIP now matters far earlier in the relationship. For the authoritative position on phased dates and qualifying periods, the ACAS guide to the Employment Rights Act 2025 changes is the reference to follow.