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 glowing, digital rendering of Earth is displayed against a dark background. The planet is highlighted in vibrant pink and purple hues, with lines and dots creating a network effect around it, illustrating global connectivity and data exchange.
Technology
Insight

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

29.10.2025
As 2025 unfolds, the technology sector stands at a pivotal crossroads. Global markets are still digesting the rapid ascent of artificial intelligence, the regulatory ripple effects of quantum computing and the accelerating race for cybersecurity resilience.
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A dark background with a web of interconnected blue and purple lines forming a network. Numerous glowing white nodes are scattered throughout the web, creating a complex, geometric pattern that suggests a digital or technological theme.
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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Two people sit at a table reviewing a document with charts and graphs. One person is holding a pen and gesturing towards the paper, while the other person points with their finger. A laptop and a glass of water are visible in the blurred background.
Public & Regulatory
Insight

Regulators go after dynamic pricing

22.07.2025
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Two people sit at a table reviewing a document with charts and graphs. One person is holding a pen and gesturing towards the paper, while the other person points with their finger. A laptop and a glass of water are visible in the blurred background.
Public & Regulatory
Insight

From safeguard to springboard: Reforms to the UK's National Security and Investment Act to boost economic dynamism

21.07.2025
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Technology
Insight

Eight key trends for the technology sector in 2025

28.01.2025
With 2025 well underway, the tech industry is bracing for transformative changes driven by, among other things, evolving regulations, ethical considerations and sustainability imperatives. Drawing on the extensive technology sector expertise from across the firm, we set out eight key trends poised to reshape the tech landscape over the next 12 months. 
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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