John Cassels | Fieldfisher
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Professional background

Professional background

I co-head the firm's Regulatory Group.  I specialise in competition law and risk management, advising on all aspects of the UK and EU regimes including cartel investigations, antitrust litigation, restrictive agreements, dominance issues, alliances, and structural changes such as mergers and acquisitions.  I also work with clients on public procurement, state aid, international trade and regulatory investigations. My advice is practical and commercial, focusing on assessing and mitigating real risks.    

I have worked with clients across a broad range of industries from water and wastewater to soft drinks. I have particular expertise in regulated sectors, including food/beverage, transport, life sciences and financial/professional services.

I have a First Class Honours Degree in Law from the University of Glasgow (Scotland) and a Masters in Law and Economics (Distinction) from the University of Rotterdam (The Netherlands).

 

Awards & recognition

Awards & recognition

Peloton Interactive, Inc.
John Cassels and the entire Fieldfisher team has been a valuable partner to us as we entered the European market. They are responsive and thorough, but most importantly they have really taken the time to understand our business, our goals, and our people, and the result is smart, practical advice even when we're moving fast. We think of them as an extension of our team and would happily recommend them
Legal 500
Very astute, approachable and adaptable

Authored pieces

All Resources
A close-up image of a metallic maze with smooth, polished surfaces. The maze is displayed in shades of purple and blue. A white arrow is seen pointing through the maze, indicating a path.
International trade
Insight

NSIA consultation response

26.03.2026
On 12 March 2026, the UK government published its response to a July 2025 consultation regarding the National Security and Investment Act 2021 (Notifiable Acquisition) (Specification of Qualifying Entities) Regulations 2021/1263 (the "NARs" ). The NARs set out the scope of sectors for which mandatory notifications must be made under the UK's National Security and Investment Act 2021 ("NSIA ").
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Technology
Insight

9 tech sector trends for 2026: regulation, resilience and recalibration

28.01.2026
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Technology
Insight

7 key takeaways from Fieldfisher’s 2025 Tech Sector GC Summit

29.10.2025
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Public & Regulatory
Insight

The cost of control: What the EU Commission's recent RPM fine means for brand pricing strategies

23.10.2025
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Public & Regulatory
Insight

Regulators go after dynamic pricing

22.07.2025
The UK Competition and Markets Authority and the EU Commission have recently confirmed that they are working on multiple (not yet public) dynamic pricing antitrust investigations. This means that we are likely to see numerous antitrust investigations launched before the end of this year, both in the UK and EU with civil actions for damages running alongside those investigations.
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What others say…

Peloton Interactive, Inc.
John Cassels and the entire Fieldfisher team has been a valuable partner to us as we entered the European market. They are responsive and thorough, but most importantly they have really taken the time to understand our business, our goals, and our people, and the result is smart, practical advice even when we're moving fast. We think of them as an extension of our team and would happily recommend them
Legal 500
Very astute, approachable and adaptable