In the recent case of Illumina, Inc and another -v- TDL Genetics Laboratory Ltd and others [2019] EWHC 1159, the High Court considered the question of whether a claimant required the Court’s permission to adduce expert evidence under Part 35 of the Civil Procedure Rules when that evidence was produced for different, earlier litigation.


The claimants’ claim alleged infringement of a patent by TDL. In order to support the claim, the claimants sought to rely on elements of the expert evidence of Dr Henry Erlich, whose evidence had not been produced for the claimants, but for the defendants in a previous unrelated claim. Illumina, the first claimant, served a hearsay notice in respect of the evidence in question.

Permission to adduce expert evidence

In a bid to prevent the claimants relying on Dr Erlich’s evidence, TDL submitted that the claimants were required to obtain the Court’s permission to adduce the report in evidence under CPR 35.4(1), which states that ‘no party may call an expert or put in evidence an expert’s report without the Court’s permission’.

The Court determined that there were two issues for it to consider:

  1. was Illumina required, under CPR Part 35, to obtain permissionto adduce Dr Erlich’s evidence, pursuant to a hearsay notice?
  2. if so, should permission be given for that evidence to be adduced?

The relevant rules

CPR 35.2(1) defines an expert as ‘a person who has been instructed to give or prepare expert evidence for the purpose of proceedings’. Dr Erlich’s evidence had been produced for defendants in other proceedings, and at first glance, one might assume that Dr Erlich would be considered an expert under that rule.

However, the Court considered the decision in Rogers and another -v- Hoyle [2014] EWCA Civ 257, in which the Court of Appeal commented that the purpose of the provisions governing experts in CPR 35 was to regulate the evidence of experts instructed by the parties, in order to ensure they acted as experts and their reports were compliant. The upshot of this, the Court held, was that expert evidence produced for other proceedings did not come under CPR 35. Therefore, Dr Erlich’s report was not to be considered to be giving expert evidence, his evidence fell outside of CPR 35 and permission was not required in order to adduce his evidence by way of a hearsay notice.

As a result, the second question above did not need to be determined by the Court.

Secondhand experts?

At first glance, this decision suggests that parties to litigation involving experts would do well to utilise their resources to find helpful evidence from previous cases, which may assist them in saving costs on expensive technical experts.

Evidently, the need for some types of expert arises more commonly than the need for other types of experts, but nonetheless, with disbursement bills for experts often running to six figures in high-value litigation, time spent tracking down useful ‘secondhand’ expert evidence may be well spent.

Importantly, however, there is a significant pitfall in seeking to rely on such evidence. As identified by the Court in Illumina, unless the party seeking to rely on ‘secondhand’ expert evidence is prepared for its author (and potentially also others mentioned within the relevant expert report) to attend Court for cross-examination, there is unlikely to be substantial weight attached to the ‘secondhand’ evidence. It is after all hearsay, and was produced for a different purpose.


For parties engaged in litigation which is similar to other litigation you have undertaken previously, it would be sensible where appropriate to at least consider the possibility of seeking to adduce ‘secondhand’ evidence. However, this is likely to be subject to the provison that it would need to be cost effective for you to do so, and that the prospective success of your case should not be overly reliant on that evidence.

Decisions relating to reliance on expert evidence should be made on the same basis as any other major decisions in litigation – after a careful analysis of the costs and risks involved.