Some authorities are better than others; and some reports of those authorities are better than others. Don’t take our word for it: the Lord Chief Justice, Lord Judge has just issued a new practice direction on the matter.
It reiterates what a previous Lord Chief Justice, Lord Woolf, said a little over a decade ago in Practice Direction (Judgments: Form and Citation)  1 WLR 194, namely that where a case has been reported in the official Law Reports published by ICLR it must be cited in preference to any other version.
We’ll be reporting it in full in the Weekly Law Reports very soon, but in the meantime here is a preview of the relevant section:
Citation of Authority
5. When authority is cited, whether in written or oral submissions, the following practice should be followed.
6. Where a judgment is reported in the Official Law Reports (AC, QB, Ch, Fam) published by the Incorporated Council of Law Reporting for England and Wales (ICLR), that report must be cited. These are the most authoritative reports; they contain a summary of the argument. Other series of reports and official transcripts of judgment may only be used when a case is not reported in the Official Law Reports.
7. If a judgment is not (or not yet) reported in the Official Law Reports but it is reported in the Weekly Law Reports (WLR) or the All England Law Reports (All ER) that report should be cited. If the case is reported in both the WLR and the All ER either report may properly be cited.
8. If a judgment is not reported in the Official Law Reports, the WLR, or the All ER, but it is reported in any of the authoritative specialist series of reports which contain a headnote and are made by individuals holding a Senior Courts qualification (for the purposes of section 115 of the Courts and Legal Services Act 1990), the specialist report should be cited.
9. Where a judgment is not reported in any of the reports referred to in paragraphs  to  above, but is reported in other reports, they may be cited.
10. Where a judgment has not been reported, reference may be made to the official transcript if that is available, not the handed-down text of the judgment, as this may have been subject to late revision after the text was handed down. Official transcripts may be obtained from, for instance, BAILII (http://www.bailii.org/). An unreported case should not usually be cited unless it contains a relevant statement of legal principle not found in reported authority.
11. Occasions arise when one report is fuller than another, or when there are discrepancies between reports. On such occasions, the practice outlined above need not be followed, but the court should be given a brief explanation why this course is being taken, and the alternative references should be given.
12. If a judgment under appeal has been reported before the hearing but after skeleton arguments have been filed with the court, and counsel wish to argue from the published report rather than from the official transcript, the court should be provided with photocopies of the report for the use of the court.
13. Judgments reported in any series of reports, including those of the Incorporated Council of Law Reporting, should be provided either by way of a photocopy of the published report or by way of a copy of a reproduction of the judgment in electronic form that has been authorised by the publisher of the relevant series, but in any event (1) the report must be presented to the court in an easily legible form (a 12-point font is preferred but a 10 or 11-point font is acceptable) and (2) the advocate presenting the report is satisfied that it has not been reproduced in a garbled form from the data source. In any case of doubt the court will rely on the printed text of the report (unless the editor of the report has certified that an electronic version is more accurate because it corrects an error contained in an earlier printed text of the report).”
Three important observations may be made.
First, although this revokes and supersedes what was said in para 3 of Lord Woolf CJ’s practice direction, it leaves intact para 2 (which deals with official neutral citations issued by the courts from 2001 onwards) and para 1 (which gives guidance on the form and delivery of judgments in the Senior Courts).
Secondly, it emphasises (in para 8), the superiority of reports produced (as all ICLR law reports are) by members of the legal profession, ie barristers or solicitors. It is worth pointing out that ICLR law reporters (who sign their own reports) attend hearings in person, and write their own reports: they are not merely a judgment collection or summary writing service. This accounts, of course, for the superiority of the resulting reports, as recognised by the long standing practice of citing The Law Reports in preference for rival series.
Thirdly, it recognises in an official practice direction the crucial role played by the British and Irish Legal Information Institute (BAILII) in collecting and making available the official transcripts of judgments delivered not only by the Senior Courts but a range of other courts and tribunals. Though these unreported judgments do not have the status of law reports, they provide an often essential and easily accessible resource for the study and practice of law, and as a charitable organisation ICLR is proud to support and co-operate with BAILII.