An issue that arises in virtually every detailed assessment, is the extent to which a paying party can pore over the file, attendance notes, advices, and other documents of the receiving party’s lawyers which may need to be produced to the court to justify the fees claimed on assessment.
Prima facie most (though by no means all) of the documents in a solicitors file will attract legal professional privilege: the maintenance of that privilege can be very important in practical terms where proceedings are not yet concluded, or there may be further proceedings.
Even if the parties are unlikely to encounter each other again, as in most personal injury claims, the maintenance of privilege concerns a client’s rights, not least to confidentiality in his or her affairs.
Legal professional privilege is a fundamental common law right upon which the whole administration of justice rests. It is not a rule of evidence or procedure. Per R v Derby Magistrates Court ex parte B  1 AC 487 the court has no power to order disclosure, of privileged material: in that case, the court observed that there was no balance of the parties interests to strike: the balance had been struck by the formulation of the doctrine of legal privilege centuries earlier.
Even where the CPR have assumed a power to order disclosure of privileged material (the former CPR 48.7(3)) that rule has been struck down as ultra vires per the case of General Mediterranean Holdings v Patel  1 WLR 272.
There has been no attempt to replace that rule and the position of disclosure of documents in the context of assessment proceedings remains that established at common law and embodied in the Practice Direction to part 47 at paragraph 13.13.
The Practice Direction applies where a claim for costs is being pursued and the court is actually being asked to make a decision on the recovery of costs but even then, the court has no power to compel a particular document to be shown to the paying party: the receiving party is free to decline to do so and seek to rely on alternative evidence to prove a claim for costs:
13.13 The court may direct the receiving party to produce any document which in the opinion of the court is necessary to enable it to reach its decision. These documents will in the first instance be produced to the court, but the court may ask the receiving party to elect whether to disclose the particular document to the paying party in order to rely on the contents of the document, or whether to decline disclosure and instead rely on other evidence.
The procedure embodied in this document, attempts to balance both the receiving party’s right to protection of his or her privilege and the paying party’s right not to pay more than reasonable and proportionate costs: the assessment of which is heavily bound up with consideration of the documentary material which would justify the claims for costs.
This paragraph of the Practice Direction reflects what has been termed the “Pamplin” procedure, as formulated by Hobhouse J as he then was in the case of Pamplin v Express Newspapers  1 WLR 689 :see in particular page 696H and 697A.
Thus even assuming that a court put the receiving party to his election to disclose the entire file of papers, the receiving party can accordingly decline to produce them. Such a decision would not be likely in practice: the Practice Direction is predicated on disclosure of “particular” documents on a document by document basis. The costs judge would have to formulate reasons for his decision and they would be subject to a right of appeal. If, in a truly exceptional case, a party was put to his or her election in respect of an entire file, he or she would still not be obliged to disclose it. But alternative evidence is unlikely to be judged trustworthy. The likely consequence would be that the Bill of Costs would be assessed at nil.
However even documents disclosed during the process of an assessment do not lose their inherently privileged nature. Longstanding authority running from the case of Goldman.v.Hesper  1 WLR 1238 to the recent decision of the Court of Appeal in the case of Dechert LLP v Eurasian Natural Resources Corporation Ltd  EWCA Civ 375 confirms that in the case of documents from a solicitors file, provided as part of the election process, the waiver of privilege is partial, not complete and limited to the particular proceedings only.
This principle has real significance in respect of further proceedings between the same parties, or rather where there are recurrent proceedings between a particular firm of solicitors and paying parties.
Sometimes an attempt will be made to use documents disclosed in other cases, or findings in judgments obtained in other cases to seek to argue that that material is probative and relevant in the unrelated proceedings. Such an approach is wrong as it ignores the limited waiver that exists in relation to documents produced during an assessment and in respect of other decisions on particular facts which raise no issue of law, is wrong in principle.
Decisions in individual cases between different parties or even the same parties are generally irrelevant where no issues of res judicata or issue estoppel arise: see the general statements of principle on the admissibility of findings of fact in other litigation in the case of Secretary of State for Trade and Industry v Bairstow  EWCA Civ 321 particularly paragraphs 15 to 27.