UK general counsel have thrown their support behind the open letter signed by 170 US legal heads warning law firms to do better on diversity or miss out on work, as talks over a similar initiative on this side of the pond get underway.

The letter, which was signed by GCs and chief legal officers from a range of companies including Cable & Wireless, Heineken and Mozilla, said their companies would divert their "substantial" legal spend to firms that commit to diversity and inclusion.

While the signatories of the letter were primarily from the US in-house community, a growing number of high-profile UK GCs have now told Legal Week that they would also sign the letter, or support a comparable initiative led out of the UK, discussions over which have already begun.

Coca-Cola European Partners GC Clare Wardle and former Royal Mail GC Maaike de Bie – who is joining Easyjet as GC this March – both told Legal Week that they were aware of talks over a UK-led effort to commit law firms to improving diversity.

Crown Estate GC Rob Booth (pictured right) was among those who said he would sign the letter. "I'd sign any document that is committed to finding a solution to improving diversity in the legal industry," he told Legal Week. "It is a massive opportunity missed if we don't recognise the value that diversity of thought can bring.

"The issues raised by this letter should be front and centre in all of our minds and I am really pleased to see it raised with critical mass. It is incumbent on us as customers to not just sign letters like this, but also to measure diversity in our value chain where we can, share that information and to deliver consistency on the buyer side; even when doing the right thing for the long-term may conflict with short-term decisions."

Others to express their support for the letter include notonthehighstreet.com GC Kate Burns, Transferwise GC Jenifer Swallow, and National Grid global head of legal operational excellence Mo Zain Ajaz.

Swallow said: "The impetus for the US letter was specific to that market. I would support a similar initiative here that was responsive to the facts and landscape of the UK market.

"The UK statistics show [that] the fantastic increase in female lawyers practising law is not yet reflected at more senior levels in law firms. There is progress on gender equality in the UK profession, but it is slow – too slow. Keeping the imperative for progress high on the agenda for firms – and in fact for wider society – is super important, and the 170 US GCs' letter should certainly help achieve that."

"No one used to feel comfortable bringing up diversity as a requirement in panel reviews, but now I mention it every time"

Michelle Fang, chief legal officer of car-sharing company Turo, who spearheaded the letter, said she welcomed support from GCs around the world and and encouraged UK legal heads to either add their signature to the letter or create their own. "Either join our letter or start your own one – whichever one you believe will be more powerful," she told Legal Week. Those interested in joining the initiative can get in touch with her via LinkedIn.

"The plan from the start was to launch this letter publicly and then for each signatory to reach out to their law firms privately to let them know what their personal expectations are of them as legal advisers, she said. "That process has already started – so far, law firms have been supportive and have welcomed the letter."

Barclays head of commercial engagement Stephanie Hamon – who has taken a lead role on the bank's efforts to push its external law firms to improve diversity – acknowledged the power that clients can wield, describing the letter as "a great initiative".

"We have gone one step further than a statement and are trying to put it in practise by adding diversity and inclusion as one of the six pillars of expectations of law firms we have for our panel firms," she added.

Other GCs across the UK are pushing forward with similar efforts, and are increasingly using their influence to encourage greater diversity in private practice.

Talking about how she assesses law firm diversity when choosing external legal advisers, Swallow said she conducts scenario-based conversations with law firms during the tender process, and observes the way they interact with each other. She said: "From this, you can tell their level of respect and decency for one another."

Pearson GC Bjarne Tellmann (pictured) also noted the importance of observing the relationship dynamics of the teams tendering for panel appointments. When listening to law firm pitches on diversity, he said he pays particular attention to body language and team interaction.

"One firm that really impressed us," he said, "brought in a junior associate and during the pitch asked them to explain why it's important for them to be in the team as well."

Burns added: "No one ever used to feel comfortable bringing up diversity as a specific requirement in legal panel appointments, but now I mention it every time."

Wardle said it is important law firms do not just turn up with a token ethnic or female team member – or treat any other forms of diversity in this way – but instead demonstrate diversity within their teams and how it adds value to them. She added law firms must illustrate the value of diversity even after the tendering process is finished – they must be able to "walk the walk after", and not instantly hand over the work to less diverse teams.

"The shift the legal world needs to take," said Tellmann, "is recognising that it's not just a good thing to do, but it's actually a smart thing to do, because teams make better decisions when they're diverse."

But while GCs are placing the onus law firms to improve, they also recognise the importance of getting their own houses in order. "We should also be doing something similar ourselves, said Tellman. "It can't be just us asking our legal advisers for better diversity, but should instead be a public pledge to strive for diversity in all legal departments."