The problem stems from an old rugby injury, and Hughes' recovery is not being helped by his intensive jet-setting programme, which has included trips to Chicago and Latvia. In fact, the garrulous, craggy-faced Scot has covered "22,000 miles in the past couple of weeks".
As you will have detected by now, Hughes is not your typical architect. Indeed, he originally wanted to be an artist, on the grounds that the prettiest girls in Dundee were in the town's art college. After he settled for architecture, his career has not followed well-trodden paths. For a start, much of what he did in his early years was in Baghdad during the early 1980s.
At the time, the city was one of the busiest construction sites in the world. Hughes, who was working for The Architectural and Planning Partnership, was rubbing shoulders with Arup Associates, Ricardo Bofill, Carlfried Mutschler and Frei Otto. He helped to design a huge mixed-use urban regeneration scheme around the Sunni mosque of Al-Gailani, and then also took over responsibility for another mixed-use project around the Shia mosque and shrine of Al-Kadhimain.
Saddam Hussein, who had recently come to power, had given one Rifat Chadirji the final say on all projects. "Presentations tended to be very nervous occasions and I remember one particularly anxious moment when he spotted that two of the toilets in more than 400 houses forming part of our Gailani project were facing Mecca.
"Perhaps because I was young and politically naïve, but I had no real sense of working within the context of a political dictatorship. On the contrary, for me the whole experience – apart from the toilets – was richly rewarding. The whole experience left me with a great appreciation of the country and its culture.
You could have a bunch of energy-efficient houses, but without transport or an actual community it’s not that much use
In 1986, he set up his own practice, Miller Hughes, with partner Bruce Miller. Since Miller's retirement in the mid-1990s, Hughes has been managing director and, until recently, he was sole owner of the the £2m turnover firm. He now intends to split the ownership of company in half, with five directors each taking a 10% stake. He is doing this to provide a cash incentive to the directors – he has set an annual growth target of 20% – and to free up time to grow his other business, a sustainability consultant called Smart Futures.
Add to this Hughes' work for UK Trade International, a governmental body that drums up work abroad for UK firms (hence the trip to Latvia). Then add to that his position on the Urban Thematic Strategy group, a European Union panel that promotes economic development in European cities. So it is little wonder that he's competing with Tony Blair in the accumulation of air miles. And, we might add, policy issues. He points to his head. "There's a lot going on at the moment."
Miller Hughes will continue to work on straightforward architecture from its headquarters in Chichester, West Sussex – it was recently involved in the early phases of Bellway's Barking Reach housing regeneration scheme. Meanwhile, Smart Futures will aim to take advantage of what Hughes believes is going to be a huge growth in demand for sustainable buildings.
The reason is that many European banks have changed their due diligence procedures to take account of environmental and social issues. "Rather than simply being interested in technical or financial matters, it's now sustainable ones as well," he says. The top 10 European banks last year signed up to the Equator Principles, set up by the International Finance Corporation in 2002. These promote the ecologically sensitive and responsible development of schemes valued at $50m (£28m) or more.
Hence Hughes' belief that such institutions need statistics and figures to work with on developments. His firm will start this autumn on a study for global property group CoreNet to find practical ways to deliver sustainability.
But what is sustainability? "Carrying out your activities in a way that balances social, environmental and economic interests so as not to disadvantage future generations," is Hughes' working definition. This is, of course, a good deal broader – and hugely more ambitious – than the way British designers and contractors usually approach the subject. "The construction sector tends to just look at photovoltaic cells or energy use," he says. "You have to step back from that. You could have a bunch of energy-efficient houses, but without transport links or the creation of an actual community it's not that much use. It's what you do after construction that's so crucial."
Given the role Hughes has carved out for himself, he's unsurprisingly wary of viewing architecture as just designing buildings – or, as he describes it, "design with a small 'd'".
Personal effectsWhere do you live? In Chichester, near the Miller Hughes office. I’ve also got a farmhouse in Tuscany and an apartment in the Alps. I’ll be back skiing soon.
What position did you play at rugby? Prop. What do you think, with a face like this?
Will the Greeks finish the facilities for the Olympics on time? They’ll be fine. Unless the buildings fall down, people will not be that focused on the facilities. The sadness is that the Greeks have not been able to maximise the long-term benefits of building the facilities in the rush to get it all done.
Will you return to Iraq? When the time is right. There are real opportunities for UK firms, especially in urban regeneration. But not yet. The prerequisite for firms working there is a stable and secure situation. A lot of people rushed over there last year but it was, and still is, incredibly dangerous.