Alleged patent infringement

Alleged patent infringement

‘I have been accused of infringing someone’s patent. What should I do?’ 

Receiving a patent infringement claim, regardless of who you are or how much experience you have, may be a shock. You might be dealing with a misconceived complaint or you have made a mistake, we can assist you in overcoming this obstacle in your company's progress. 

Before you contact a patent solicitor 

  • Don't be alarmed – this happens to many hardware and technology companies at some point in their journey. 
  • Do not respond – yet – even to 'without prejudice' letters without first consulting with an IP solicitor. 
  • Set any deadlines referenced in the letter, diarise some time to deal with this matter and have a conversation with an IP solicitor as soon as possible. 

At this point, you may be weighing up whether to reduce risk by stopping selling, offering for sale, or importing the allegedly infringing product or stop using the allegedly infringing process – if this is possible. If you are considering this route, our corporate, commercial and civil litigation colleagues will support the IP team in advising whether this could impact on your existing contractual obligations. 


Once the letter comes to our patent litigation attorney, we will triage the situation – establishing whether there is a real risk of imminent litigation and if so in what jurisdiction, for what cause and with what consequences.  Then we will help you form a strategy. 


A good strategy is a logical result of: 

  • Identifying what this claim means to you and 
  • Understanding what is likely to happen next. 

This requires teamwork. Here are just a few of the questions our experts will consider – some you will answer, some we will: 

The Accuser

  • Who sent the letter? Solicitor? Business owner? The attorneys who drafted the other patent? What is their reputation? What country are they in?  
  • What’s the backstory? Is there a prior relationship? The hardest patent disputes are often between people who once worked together 
  • Will you come across the complainant again in future? How? Is this a tight-knit industrial sector or are these people you never heard of? 
  • Has the complainant got deep pockets? Has the complainant got investors with their own agenda? 
  • Are they threatening to seek a court order to stop your activities until the case settles (an interim injunction)? 

The Complaint: 

  • Does the complaint appear well-founded, a try-on, or somewhere in between? 
  • Are all the legal hurdles for patent infringement addressed? Accurately?  We will work through these and spot gaps. 
  • Have they supplied evidence? Would it stand up in court? 
  • Can we see some procedural hurdles to put in their way? If so, would this serve a long-term commercial purpose?  
  • Which of our hundreds of previous cases does this most closely resemble? 
  • Realistically, what would the IP judges we appear before make of this? 


  • What resources of time and money do you have to fight this? 
  • How high are the stakes for you and the complainant? 

The Patent and the Counterclaim: 

  • In most patent cases, a counter-attack of some form is mounted to revoke or invalidate the patent relied on, or to contest its ownership 
  • Most patents are members of families extending beyond the UK – any of them might be liable to attack through procedures within the patent office where they are proceeding such as observations, opposition, or revocation actions.  
  • If UK proceedings are issued, the majority of defences are accompanied by a counterclaim asking the court to invalidate the patent relied on (rendering it null and void).  
  • Invalidity counterclaims usually invite the court to find that the patent was not a true invention, either because it lacked novelty or because it lacked a inventive step.

Remember, to find the right strategy, you and your patent solicitor must exchange information until you establish what this inbound accusation means for you and whether you have the resources to mount an outbound counterclaim.  The right answer may lie outside the field of patents altogether and we will bring in civil litigators to support us on any contract or misrepresentation claim that you may be able to bargain with.  

The response to a patent infringement letter 

Our next steps will take into account the many similar cases we have seen before.  Sometimes the most sophisticated strategy results in a short letter – sometimes you won’t even tell your accuser that you are represented. Sometimes attack is the best form of defence.  Sometimes a show of respect is required to smooth troubled waters. What we can promise is that the strategy will be tailored to you. 

In the limited number of patent cases that go to court, accusers need to show that: 

  • They have a valid patent which is in force 
  • You have done something which infringes that patent without their consent 
  • What you did is connected to the target jurisdiction 
  • There are no statutory exceptions or defences available to you 
  • They are the people entitled to a remedy 
  • (If they want an injunction) you intend to continue doing what they complained of 

Paying damages usually wouldn’t be dealt with by a court until all the questions above had been dealt with – usually at a second trial.  The legal costs of the patent battle itself often loom larger than the eventual theoretical damages award and that is why our low cost model can give you an advantage in this struggle.  

To find out more about patents, read our patents: FAQ’s guide.

About our expert

Lindsay Gledhill

Lindsay Gledhill

Intellectual Property Partner
Lindsay Gledhill is an Intellectual Property Partner at Harper James. She has specialised in intellectual property exploitation and dispute resolution since 1997. She trained and qualified in Cambridge’s top intellectual property firm during the 'dot com boom', then spent four years at top 50 firm, Walker Morris.

Our offices

A national law firm

A national law firm

Our commercial lawyers are based in or close to major cities across the UK, providing expert legal advice to clients both locally and nationally.

We mainly work remotely, so we can work with you wherever you are. But we can arrange face-to-face meeting at our offices or a location of your choosing.

Head Office

Floor 5, Cavendish House, 39-41 Waterloo Street, Birmingham, B2 5PP
Regional Spaces

Stirling House, Cambridge Innovation Park, Denny End Road, Waterbeach, Cambridge, CB25 9QE
13th Floor, Piccadilly Plaza, Manchester, M1 4BT
10 Fitzroy Square, London, W1T 5HP
Harwell Innovation Centre, 173 Curie Avenue, Harwell, Oxfordshire, OX11 0QG
1st Floor, Dearing House, 1 Young St, Sheffield, S1 4UP
White Building Studios, 1-4 Cumberland Place, Southampton, SO15 2NP
A national law firm

To access legal support from just £145 per hour arrange your no-obligation initial consultation to discuss your business requirements.

Make an enquiry