The rule of witness immunity was set out by Lord Hutton in Darker v Chief Constable of the West Midlands [2001] 1 AC 435, a case which concerned police malpractice.

Lord Hutton held: ‘The rule that a party has immunity in respect of what he says and does in court has been established for centuries.’

Lord Hutton went on to acknowledge in Darker that the rule had boundaries and that immunity did not, on the facts of Darker, extend to things allegedly done by police officers during the investigation process which could not fairly be said to form part of their participation in the judicial process as witnesses.

In particular, it did not extend to the fabrication of false evidence.

Recently, the rule of witness immunity was considered by the Court of Appeal in Autofocus Ltd v Accident Exchange Ltd [2010] EWCA Civ 788, which concerned the scope of the rule in the context of business malpractice and which is relevant in civil cases.

Accident Exchange Ltd (AE) provided cars to drivers whose vehicles had been damaged in road traffic accidents caused by the negligence of other drivers.

Autofocus (AF) provided evidence for insurers of negligent drivers who wished to limit their liability for hire charges to the market hire rate at which an equivalent vehicle could be hired.

The insurers of the negligent drivers relied on AF to provide them with material with which to contest the perceived inflated elements of the hire charges claims.

AF obtained its information from rates surveyors, who provided evidence of relevant spot hire rates on the basis of information obtained in telephone calls to a number of car rental companies.

The rate surveyors would then produce a witness statement within which they would describe the process of obtaining the information.

Relevant exhibits would also be referred to in the witness statements.

AE brought a claim against AF for conspiracy to use unlawful means in obtaining evidence and deceit. AE alleged that the rate surveyors had put forward fraudulent information and that this was an integral part of AF’s business.

In an attempt to bring the matter to an end, AF applied to the court to either have the claim struck out or, alternatively, for summary judgment by reference to witness immunity. AF’s application was dismissed at first instance.

The matter proceeded to the Court of Appeal.

Lord Justice Maurice Kay turned to the principles of Darker in which the House of Lords drew a distinction between statements made by police officers before giving evidence, where the functions they performed could be said to be those of witnesses or potential witnesses, and their conduct at earlier stages in the case when they were performing their functions as enforcers of the law or as investigators.

The court held that the rule of witness immunity only extended to those acts done as part of the judicial process and was not wide enough to cover all acts which did not form part of that process. This included the fabrication of evidence.

Maurice Kay LJ was of the opinion that if the rate surveyors were found to have fabricated evidence then the principles of Darker would take effect and witness immunity would not apply.

This would be the position whether the evidence was in the form of a witness statement or exhibits.

However, Maurice Kay LJ added a word of caution in deciding the scope of witness immunity without a court hearing the complete evidence in the case: ‘In order to apply the Darker principles, it will be necessary to consider precisely what each rate surveyor and his superiors did or imitated to do and what their state of mind was at the time.

'It may be necessary to consider the chronology of the events from the phone calls... to the spreadsheets, to the creation of the witness statements.’

Although a rule which seeks to protect witnesses who are engaged in the judicial process, the rule of witness immunity has legitimate and necessary limits.

Only witnesses or potential witnesses whose actions can be said to relate to the judicial process will benefit from the protection of the rule.

Therefore, careful consideration must be had as to the nature of the allegations against a particular party and whether an application for witness immunity can be justified on the facts of a particular case.

A failure to do this from the outset will inevitably result in wasted cost and time.

Masood Ahmed is a senior lecturer in law at Birmingham City University