Out of the shadows: Advisory experts in Competition Appeal Tribunal cases

In summary

• The Competition Appeal Tribunal (CAT) has provided guidance concerning the independence of expert evidence 
• Yet lawyers still need ways to test their arguments and theories, analysing opposing expert methodologies and model scenarios 
• Shadow experts not tied by independence requirements can help resolve this tension, providing a vital strategic tool, without compromising the independent expert 

The CAT has recently tightened expectations around expert evidence and, in doing so, reshaped the strategic landscape for lawyers. After a series of cases where expert reports blurred into advocacy, the tribunal has made its position unmistakably clear: Independence is not a formality; it is the core of admissible expert evidence. 

This is reinforced by the CAT’s 2025 practice direction, which insists that experts must assist the Tribunal rather than try to advance a party’s case. The independent expert must remain unimpeachably neutral, significantly constraining legal teams’ use of them.  

Yet the dispute still demands deep analytical work, scenario testing and strategic modelling. Consequently, shadow experts, otherwise known as advisory experts, have become indispensable. 

The CAT’s recent interventions reflect a broader judicial frustration with expert evidence that reads like submissions. The Tribunal has emphasised that: 

• Experts must provide objective, impartial analysis, rather than advocacy 
• Reports must be tightly reasoned, not sprawling or argumentative 
• Methodologies must be transparent and defensible, not reverse‑engineered to support a preferred outcome 

For lawyers, this creates a structural tension.  

They still need to explore alternative theories, test causation pathways, interrogate quantum assumptions and understand the weaknesses in their own case. The insistence that the expert witness then must provide objective, impartial analysis may mean they are not best placed to undertake this exploratory work. 

Shadow experts resolve that tension by providing a protected analytical environment, in which they are free to pick holes in and test the case to be presented.  

Operating outside the Civil Procedure Rules (CPR) Part 35 and CAT’s independence framework, shadow experts have significant freedom to support the case strategy: 

• Stress‑testing liability and causation theories before they are committed to pleadings 
• Modelling quantum scenarios to understand value ranges, sensitivities and funding implications. 
• Analysing opposing expert methodologies and identifying their weaknesses without exposing the independent expert to an adversarial strategy 
• Supporting settlement strategy with robust best and worst alternative to negotiation (BATNA and WATNA) modelling grounded in financial and economic reality 

All this work is essential, but it cannot be done effectively by the independent expert without risking accusations of partiality, especially in the post‑2025 CAT environment. 

In competition damages, shadow experts can materially shift the trajectory of a case. They can map causation pathways and quantify where factual disputes genuinely affect loss. They can build financial or econometric models for scenario analysis,  (which can later be shared with the independent expert for consideration). 

They can also identify inconsistencies between pleadings, disclosure and expert reports, and support targeted procedural steps, such as focused disclosure applications or Part 18 requests. Finally, shadow experts can help clients and funders understand risk‑reward profiles with far greater clarity. 

In short, the shadow expert can serve as the analytical engine room for a dispute. It’s an essential function, but it must be kept separate from the independent expert’s formal role. 

There are several keys to maximise the value of a shadow expert while protecting the independence of the CPR 35/CAT expert: 

• Engage the shadow experts early, before pleadings harden and before instructing the independent expert  
• Define roles clearly, so that the shadow expert explores and supports strategic analysis, while the independent expert opines. 
• Use multidisciplinary capability so forensic accounting, valuation, economics, sector expertise and data analytics work together 
• Maintain clean lines of communication, ensuring the independent expert is insulated from adversarial strategy 

This approach aligns with the CAT’s renewed emphasis on independence but gives legal teams the analytical firepower they need. It reflects CAT’s clarity that expert independence is non‑negotiable, without leaving counsel to operate without technical insight.  

Shadow experts can provide the strategic depth, modelling capability and early‑stage analysis that modern disputes demand without compromising the credibility of the formal expert. It separates independence from strategy and should enable dispute lawyers to negotiate better settlements, avoid weak claims and walk into trial with fewer surprises.