But this is the aim of any specialist in facilities management: to look after their clients’ buildings in such a way that this vital, constant work doesn’t interfere with the companies’ core business.

“We are there to ensure our clients can run their business without distraction,” says Walton. “If their building runs smoothly without them even realising, we’re doing a good job.”

Facilities management (FM) has become big business over the past 15 years or so – and Optimum’s customer-focused approach has established it as one of the sector’s fastest-growing specialists.

“FM is past its infant stage but is still a very young industry,” says Walton. “Companies used to do all their building maintenance in-house, with maybe a couple of general engineers, but then pay for an expert to come in every time they couldn’t fix something. Over the past 15 years, more and more organisations have realised the benefit of an ongoing contract that covers all elements of the building.”

Optimum began 30 years ago as an air-conditioning company but now specialises in ‘hard’ services, which also include heating, refrigeration, mechanical and electrical maintenance, energy systems and IT hardware management. It also serves some impressively prestigious clients and looks after such London landmarks as the Leadenhall Building, the Bloomberg headquarters, and the Wellcome Trust’s premises on Euston Road.

But its clients come – literally – in all shapes and sizes, says Walton. “Every building is different and every business has different priorities so we tailor-make bespoke packages.”

The first step is an assessment of the building, which, he says, is a learning curve for everyone. “We quite often find the clients don’t know their buildings as well as they think, particularly if they haven’t outsourced maintenance before. We establish where the systems are, the strengths and the vulnerabilities, and what action we’ll take if an asset breaks or needs replacing, often revealing things the client hadn’t thought of.”

And the very idea of how to look after a building is changing. “Facilities management used to be just about buildings,” he says. “Now everyone’s realised the focus should be on people, and how the building looks after them. We understand there’s a clear correlation between, for instance, airflow, lighting conditions and people’s ability to work at their peak. We now use employee habits as the focus of maintaining a building, to ensure they are looked after.”

There are other factors too. “There’s much more of a focus now on energy management and sustainability, and that links into technology and smart buildings. We can do data analysis to question whether a particular bit of kit needs to be working as hard as it does, or even at all at, say, 2am, and if and how it can run more efficiently.”

It’s also about identifying problems before they happen. “We run building management systems (BMS) that identify issues, and work with a tech partner to provide what we call an ‘omnibox’ that plugs into the BMS and ‘tracks’ the building.

“And we’re also currently working with a client to develop computer-aided facilities management (CAFM) software to link the BMS with a dashboard showing real-time data, so companies can monitor their own building to ensure it’s statutorily compliant, if there’s any planned preventative maintenance and so on. If, as we hope, we get that up and running, it will be a game changer.”

This puts Optimum at the forefront of building-management innovation, but Walton says it also reflects higher client expectations – and those expectations can make recruiting a challenge. “Expertise is our USP and we have to work hard to maintain that specialty,” he says. “Clients demand the best but, as in many industries, it can be a struggle to find potential employees with the high level of skills we need.”

But Optimum is meeting the challenge, in part through a strong staff-development programme. “We are proud of our apprenticeship scheme. We have 15 apprentices dotted around the business. Our two partners [John Crehan and Jim Moore] both started out as engineering apprentices.”

Optimum sets great store by diversity, too, right through the company, partly demonstrated by its three female board members and those new young recruits. “It is a male-dominated industry,” says engineering apprentice Rebecca Homden, “but that doesn’t mean I can’t do the job. The company has been hugely supportive of me and I believe my managers want to see me succeed. I feel that once I qualify I’ll be encouraged to take the next step in my career, whatever it may be.”

And it seems there will be plenty of opportunity: in just the last four years, the firm has more than doubled its staff from 205 to 471, and its turnover from £32m to £67.2m. “We’re in a great position,” says Walton. “Bigger than the companies we were pitching against four or five years ago, and now able to compete against the really big boys. And because of the way we’ve grown, we’re flexible enough to do a contract, whether it’s £200,000 or £5m.”

And the growth is planned to continue – as the company gets a new building of its own. “RBS has provided a commercial mortgage for a new head office in Olney [in Buckinghamshire],” says Walton. “This will allow Optimum and our sister company Eighty Seven Holdings to restructure our back-office operations through a centralised approach, allowing us to more easily share resources, skills and knowledge, which in turn will result in cost savings for the business.

“We’re largely based in London at the moment but we do have a small operation in Manchester and pockets of contracts in Bristol and elsewhere, so we’re looking to expand geographically. But the design and requirements of buildings are changing too – more companies are building data centres so we want to be involved in them.

“Facilities management is changing and developing all the time, as people learn more and more about what their buildings can do and how they can and should work. We are working hard to ensure we are right at the forefront of these developments. It’s an exciting place to be.”