Meet the team: Callum McGuinn, Partner and Patent Attorney in the Chemistry team, London

As part of our 'meet the team' series, we talk to Callum McGuinn about his journey to becoming a patent attorney, the future of battery technology and why he is running the London Marathon.

After finishing his Master’s degree in Chemistry, including a year spent in research, Callum decided academia wasn’t for him and started exploring other possible careers. 

Like many of his Oxford peers he considered joining one of the big banks or going into management consultancy, but it was a career as a patent attorney that appealed to him the most. 

“I’ve always enjoyed finding out about new research, digesting it, understanding it and really getting to grips with it on a technical level,” explains Callum. “I applied for a trainee patent attorney position at Mewburn Ellis and when I went to the interview it was like a breath of fresh air. I was speaking to people like me who loved to talk about new developments in chemistry and how they worked. I came out of the interview knowing it was the right job for me, so was over the moon when they offered me a position.”

Ten years on and Callum is now a partner at the firm. “The great thing about being a patent attorney is that you get to see real results from the effort you put in,” he says. “The patent office will send you a letter saying one of the patents you worked on has been granted or, at the end of an eight-hour opposition hearing, you will have confirmation that you’ve won – that they were persuaded by your arguments. That’s a really good feeling.”

He also loves the “penny drop moment that comes when, after spending time trying to get your head around a technical issue, it suddenly all comes together and makes sense.”

Your strongest arguments

Experienced in oppositions, Callum explains the importance of identifying your strongest arguments and focusing on them. “Like any advocacy situation, when it comes to persuading the opposition division or appeal board, you need to identify the best arguments you have on each issue. You might have 15 in your favour but only five of them will be strong enough to have a chance of winning the point,” he says. 

“If you run through every possible argument, you’ll be in danger of losing, boring or confusing the judges. It’s a real challenge to identify which are which but by rejecting the weaker arguments to focus solely on your strongest, you put yourself in a far better position.”

When given notice that an opposition is being brought against your patent, it pays to be pragmatic, says Callum. “Identify where the weaknesses of your case lie at the outset. Don’t look at your case through rose tinted spectacles – you only have four months in which to take action so use that time to work out the patent’s weak points, anticipating problems and taking mitigating action as early as possible by having properly drafted fall back positions in place.”

Callum also recommends investing in a good quality prior art search before opposing a competitor’s patent. “Even if you have good arguments, poor documentation can still let you down,” he says. “Undertaking a prior art search and reviewing all the documents in advance to find the most relevant increases your chances of achieving revocation of the patent.”


One of Callum’s recent oppositions involved a polymer manufacturer client which develops polyethylene films for packaging food products. Like many manufacturers in the sector, developing sustainable packaging that can be easily recycled is a high priority.

The company had patented a fully recyclable stand-up pouch – the kind that tend to contain baby food or cat food. “This was a real step forward,” explains Callum. “Traditionally, because these pouches need to be both rigid and protect the product effectively, they contain a metallic layer as well as a plastic outer layer, making them impossible to recycle. Our client had developed a new kind of pouch made entirely from layers of different types of recyclable polyethylene.” 

Callum defended the patent when it was opposed and won, maintaining it without any narrowing or limitation. “It is always good to win,” he says, “but even more so when it helps bring a sustainable product closer to market.”

Future disputes

One of Callum’s areas of expertise is battery technology. Research and innovation in the field is seeing an exponential rise, driven by the growing popularity of electric vehicles. “There is still a long way to go to improve the performance of batteries,” he explains. “Competition is only going to get more intense and as increasing numbers of companies jostle for position, the coming decade will inevitably see a rise in related IP disputes.”

Compared to sectors like pharmaceuticals or engineering, there are still a relatively low number of oppositions in battery technology, perhaps surprising given how rapidly the sector is developing.

“There are a lot of SMEs operating in the field, so it may well be that many don’t have the resources, knowledge or perhaps the understanding of why it’s so important to monitor your competitor’s intellectual property activity,” says Callum. “No doubt this will change as the sector grows and evolves.”

Stepping up to the challenge

Outside work Callum enjoys cycling, swimming and running, “I’ve run half marathons, but this year I’m taking it a step further, running the London marathon. My brother and I will be running together, raising money for Wigan & Leigh Hospice which looked after our grandad at the end of his life. It’s a daunting prospect but I’m looking forward to the challenge and to supporting a charity that means a lot to me and my family.”