Show and tell: the changing face of disclosure in UK tax litigation
Published on 17 September 2026
Parties are seeking enhanced disclosure in complex employment tax cases, raising questions about mass assessment regimes
At a glance
In complex employment tax cases involving mass assessments, parties are increasingly seeking enhanced, civil procedure-style disclosure.
A recent Upper Tribunal ruling confirms there is no general principle of reciprocity in disclosure orders.
Engaging a litigation strategy early, before formal proceedings begin, is increasingly important for managing costs and risk.
Tax litigation has long operated under a more limited disclosure regime than civil litigation. In the First-tier Tribunal (Tax Chamber), each party is ordinarily required to list only the documents it intends to rely on: the assumption is that HMRC will already hold the material gathered during enquiry. However, this does not always hold in complex cases, particularly those involving mass assessments under employment tax regimes such as the off-payroll working rules.
Enhanced CPR-style disclosure
Parties are making increasing use of the First-tier Tribunal's broad case management powers to apply for enhanced, Civil Procedure Rules-style disclosure in circumstances where it has assessed large numbers of taxpayers.
Employment tax regimes are particularly prone to this development, including the agency worker rules, managed service company rules and off-payroll working rules. The extension of the off-payroll working rules to the private sector in April 2021, together with the new umbrella company rules effective from April 2026, is expected to generate further litigation and with it more disclosure applications.
HMRC knowledge
Where HMRC seeks enhanced disclosure to establish the factual basis for mass assessments, a fundamental question arises: if HMRC lacked sufficient information to assess on a properly informed basis, are those assessments vulnerable on best-judgment grounds? HMRC's own operational guidance contemplates using tribunal directions to obtain information after assessments have been issued, a practice that sits uneasily with separate guidance emphasising the need to gather adequate material before proceeding to assessment.
In HMRC v Ducas Ltd [2025], the Upper Tribunal rejected HMRC's argument for a general principle of reciprocity in disclosure orders, confirming that the First-tier Tribunal's case management discretion is broad and that disclosure obligations must be assessed on the particular circumstances of each party, not by reference to what has been ordered against the other side.
Osborne Clarke comment
As tax disputes grow in volume and complexity, building disclosure into a litigation strategy from the enquiry stage onwards is becoming a practical necessity for those facing mass-assessed employment tax cases.
For further analysis of the changing face of disclosure in tax litigation and what these developments mean for taxpayers, see "Show and tell: the changing face of disclosure in tax litigation" by Osborne Clarke's Jack Prytherch and Yousuf Chughtai and published in the Tax Journal (available to subscribers).
