"People tend to not quite understand exactly what the role of chief of staff entails. A lot of people think it sounds like the White House chief of staff, but it's really not like that," says Heathrow Airport's Carol Hui.

This January, after eight years as Heathrow Airport Holdings general counsel, Hui's remit was significantly expanded. She already sat on the executive board, but she has now taken on the additional title of chief of staff, bringing her closer to the heart of the company that runs Britain's largest airport.

So what does her new role actually involve – and why give it to a general counsel?

The chief of staff title, as Hui indicates, is often associated with government, the military or medicine, but is rarely used by big corporates. However, the role is more akin to a general counsel than one might initially think.

Hui explains: "There are not many GCs who are also chiefs of staff – in fact I don't know that there are any. But people often don't realise that a GC does more than just day-to-day legal work. I think the name 'general counsel' illustrates that – it is about giving the board and the business wide-ranging, strategic counsel.

"It is also about protecting and enhancing the reputation of the business and foreseeing both risks and opportunities – something that as a GC I am used to doing. This is the golden thread that runs through the different departments that form the function that I lead."

There are four main departments under Hui's new remit. The first continues to be the legal affairs function, which covers operational issues, competition law, commercial, IT, property and major infrastructure and capital works, corporate, financing work and company administration.

The second department that Hui continues to look after is the assurance team, which deals with internal audits, assurance and risk. Both departments are well within the boundaries of what you would expect a GC to deal with.

However, her new title has handed her responsibility for two other departments; one being Heathrow's communications function, which, according to Hui, encompasses "internal communications, but also external communications – external affairs, policy, public relations, government relations, stakeholder management, media, PR, and filming".

The other part of her expanded remit involves Heathrow's sustainability function. This focuses on areas like environmental management, air quality, climate change, carbon, noise, water, and biodiversity – considerations brought to the fore by the airport's controversial third runway plans. Hui is working with the board on how best to approach these issues, and the airport has has set out a goal to achieve carbon-neutral growth from the new runway.

Despite the seemingly mammoth responsibilities involved in the new role, Hui is exuberant about it. "It is very interesting, it's very challenging and it's very exciting," she says, while acknowledging the increased demands on her time: "I could wish for 48 hours in a day, but that's just not going to happen."

To help her manage these responsibilities, four of her in-house legal team have taken on specific remits. Irina Janakievska is now head of legal for corporate matters, with Mark Oliver head of legal operations and Jason Street head of legal for commercial affairs. Hui is also recruiting a head of legal for the third runway expansion.

"If you have the right quality of people and the competence is there, it is about delegating work to people who you can trust and who are accountable for what they are empowered with," she says. "It is not like the Wild West – the people in the team know that when they are given the authority to do things, they exercise that authority wisely."

Overall, the airport's in-house team remains relatively small, with just 10 lawyers. During Hui's time at Heathrow this number has not changed much, and is not likely to be vastly added to. "We tend to have very experienced in-house lawyers and they are broad-shouldered. We also use an external panel and we have got trainees from those panel firms. We have around six to seven trainees at any one time, and that adds to the complement of people in the legal function."

The panel, which was last reviewed in 2013, currently includes Allen & Overy, Berwin Leighton Paisner (BLP), Blake Lapthorn, Brodies, Eversheds Sutherland, Freshfields Bruckhaus Deringer, Herbert Smith Freehills, Morton Fraser and Pinsent Masons.

BLP and Pinsents were also recently appointed to a sub-panel set up to deal with legal issues specifically related to the third runway, and this high profile project is likely to be at the top of Hui's agenda for some years. Despite the size of the task at hand, Hui is focused on the present. "At the moment, it is important that the legal function as a whole understands their purpose, their vision, what the critical success factors are and how we support the business," she says.

"I need to make sure that this is done well, and that I am able to lead the team well. Rather than saying in 10 years' time, 'this is where I am going to be and this what I going to do', let's just make sure that at this moment in time, this is going to be successful."