Britain's accountancy watchdog has slapped PwC with a £5 million fine for "misconduct" in relation to its 2009 audit of Connaught.
The Financial Reporting Council (FRC) said that PwC and Stephen Harrison, a retired audit partner at the firm, have been "severely reprimanded" following an investigation.
Mr Harrison has been fined £150,000.
The reprimands relate to PwC's audit of Connaught, a FTSE 250 company which went into administration in 2010.
The misconduct charge relates to three audit areas - mobilisation costs, long-term contracts and intangible assets.
PwC has also been ordered to pay the FRC's legal costs and to make an interim payment on account of £1.5 million.