John Hayes

About

Constantine Law – the UK’s premier employment law boutique – was founded by John Hayes, one of the UK’s leading employment lawyers who is recognised in the Legal 500 and Chambers.  

John advises UK corporates on their employment law issues in the financial services, recruitment, tech and construction sectors and senior executives requiring high-level employment advice on a wide range of issues. 

He has years of experience litigating in the Employment Tribunal, and the Employment Appeal Tribunal in unfair dismissal, whistleblowing and equal opportunities cases. 

Tenacious and direct, John is also one of London’s leading solicitors in restrictive covenant disputes and an experienced High Court practitioner. He has obtained numerous injunctions for a range of corporate clients in the High Court in recent years, including in employment agency, wealth management and retail sectors. During 2025, he represented a national employment agency business in the Court of Appeal on an employment status case.  

John is also highly sought after for his experience in the arena of a-typical working, including consultancy agreements, IR35, CIS and the tax implications of each. He works closely with leading accountants to provide joined-up solutions for his clients. 

During the past year he has represented and won in the High Court for three high profile senior executives including in the Tom James -vs- Max Potter case, which was widely reported in the national and legal press. 

John completed six High Court injunctions during 2025 and is currently acting in London’s biggest whistleblowing case. 

John and Constantine Law are active members of the Employment Lawyers Association and John is a mentor to younger lawyers through ELA. He has also appeared on various ELA working parties, including the current Government consultation on restrictive covenants.  John qualified as a solicitor in 2001 and as a barrister in 1993. 

John counts as his client base some of London’s best established and owner-managed recruitment, construction, legal, wealth management and public affairs businesses. He is an entrepreneur and he networks with and supports the work of our entrepreneurial community. Constantine law is an integral part of that community. 

John writes regularly in the national and trade press on employment law subjects and you can access some of these articles here. He contributes regularly on the TV and radio and hosts an employment law podcast with Global HR leader Amanda Rajkumar, where they discuss employment trends and the challenges facing modern workplaces.  

Testimonials:

“John Hayes is very commercial, handles clients very well and gives them confidence. He always goes out to bat for the client and is very good with them.” 

– Chambers 2026 

“He is a wonderful person to have in your corner and I think genuinely cares about securing outcomes for his clients. John handles all of our restrictive covenant cases and has obtained a number of injunctions for us in the High Court to enforce restrictive covenants.” 

– Owner manager of the UK’s largest privately owned recruitment and employer agency businesses  

“John Hayes has been outstanding throughout. His leadership, clarity and attention to both detail and big-picture strategy are consistently impressive.” 

– Managing partner, Tier 1 ranked solicitor’s firm 

“I thought John was fantastic from the off, and felt a huge layer of support and confidence that was exactly what I needed to feel at the point in the process. Working with him was fast paced, efficient, with a strong approach that I greatly admire and trusted. We have ended up in a fantastic position and I will forever be grateful for his work. Constantine Law are best in class and I highly recommend working with them.” 

– Publishing executive director