Adam Sampson's electronic diary is flickering on his computer screen. If it were a person, it would look anxious. The screen is packed with shaded squares alerting him to the multitude of meetings in the week ahead. "I've got just 15 minutes free today," he says with a resigned shrug. "Busy. I'm just always so busy."
Since taking up his role as director of Shelter, the country's largest homelessness charity, just over two years ago, he has been especially active, an almost ubiquitous presence, popping up regularly in the media to comment on every conceivable aspect of housing policy and homelessness, as well as to launch a swath of new campaigns.
He has also been attempting to navigate the charity through a critical stage in its development. Sampson says he joined it at a time of great uncertainty. The number of people living rough on the streets - "the image people have traditionally equated with homelessness" - has fallen dramatically in recent years. The result is that charities in the homelessness field have had to confront uncomfortable questions about their purpose and role. Shelter, he says, has had no choice but to reinvent itself.
Under Sampson, Shelter's response has been to embrace a wider remit. In the past year in particular, it has been campaigning on "middle England" concerns, such as the effects of rampant house price inflation on first time buyers, and rural housing shortages. The charity has also, through its persistent lobbying, played a key role in shaping the deputy prime minister's house-building initiatives.
Charting a new direction has been anything but smooth. For example, it is clearly not in Shelter's interest that while it estimates there to be a quarter of a million people currently homeless in the UK, its rival, Crisis -with whom an attempted merger in 2001 failed acrimoniously - puts the figure at double that, while the government's estimate is 100,000. Sampson admits it does not look good to be disagreeing on such a fundamental point.
The biggest hiccup came last month when a linchpin of his strategy came in for some scathing criticism from the environmental charity, Friends of the Earth. The group accused Sampson of allowing Shelter to be "duped" by big business - large construction firms - into becoming part of a coalition promoting the building of more private houses in south-east England.
The coalition, backed by the deputy prime minster, John Prescott, and which also includes the Confederation of British Industry and housebuilders George Wimpey and Wilson Bowden, came together at the end of last year to persuade the government to implement the Barker report. It recommended 120,000 new private homes be built annually for the next five years.
FOE, in alliance with the Campaign to Protect Rural England, savaged Shelter's involvement and ridiculed Sampson for jumping on board, claiming the coalition's proposals were nothing more than "Mickey Mouse" economics and a threat to the countryside. "Shelter has been duped into thinking that simply building more houses will lead to the removal of people from housing and homelessness lists," an FOE spokesman said. "There is a need for more social housing but builders want to build executive homes that do not address this need."
Sampson refutes the implication that he has in some way sold out. FOE "is entitled to its point of view", he says. "I don't want to pick a fight. We share many of its environmental concerns." The coalition is "just a starting point", he suggests. "The fact is that there is a severe housing shortage. When it comes to building new homes, the big questions remain: should money be being spent on social housing for the poorest, or should it be spent on facilitating low-cost homeownership for key workers?"
But don't the critics have a valid point? Shouldn't Shelter be focused on campaigning for more social housing? Sampson says the charity has been vociferous in its criticism of the government's failure to dramatically increase spending on social housing. A dialogue with builders, he says, is "a necessary part of reaching a solution to the wider crisis".
Sampson is open to listening to his critics, but is certainly not shaken by them. He has experience of tackling challenging jobs and rolling with inconvenient political punches. His first job after university was "an extremely draining experience" as a probation officer for Winston Silcott, jailed for the killing of PC Keith Blakelock in 1987 and cleared almost five years later.
During his three-and-a-half years as deputy prisons ombudsman at the Home Office in the mid-1990s - when Michael Howard, the then home secretary, identified him as as potential troublemaker and tried to sack him before he'd even started - Sampson survived what he calls the "daily grind" of battling with bureaucracy.
His periods "inside the system" have proved valuable, Sampson says, but he relishes what he sees as his true calling: campaigning. He feels he was meant to do the job at Shelter and has no intention of being distracted from taking the charity in a new direction. "I am conscious that, over the few years before I arrived, Shelter had been very effective [at lobbying behind the scenes]," he says. "My predecessor [Chris Holmes] had huge reach into the upper echelon of government, and Shelter's ability to arm-twist ministers was unparalleled.
"What I've been trying to do, while hanging on to that, is to refresh the public campaign face of the organisation. Sooner or later, you have to beat up ministers publicly. To be effective, you have to show that you speak for a wide constituency of potential voters."
So is this partly where the decision to go down the route of campaigning on broader housing issues came from? "Absolutely," Sampson says. "What we are trying to show is that the housing crisis has manifestations beyond one marginalised group in society. It also has manifestations for mainstream voters. The social and political consequences of poor or overcrowded housing are far reaching."
Sampson insists that all this is not a distraction from Shelter's core ethos of campaigning for people who are destitute and living rough. A key part of Shelter's role in the coming months and years, he says, will be to point out to government that housing policy is inextricably linked to other social policies and has a function in helping to reduce social exclusion.
"If people are living in poor housing conditions it has an impact on child poverty, on educational attainment and on many other areas," he says. "The images that launched Shelter were not of teenagers in cardboard boxes. They were images such as the final scene of Cathy Come Home, where the kids are being taken into care. It is images like this that are closer to what we are having to deal with today."
Sampson's vision for Shelter is rooted in changes facing the whole voluntary sector. He says that as the sector as a whole moves increasingly towards "centre stage in delivering social care", charities need to ensure that they "don't lose sight of their purpose" and stay focused on campaigning for what people need.
"It is the job of voluntary organisations to offer solutions, not just to point out the problem," he says. "The battle now in housing is to establish the priorities for action. An adequate supply of good quality, affordable housing that is sustainable, and that has proper infrastructure around it, is what is needed."
Shelter says £3.5bn a year is needed to get to grips with the current shortages. "It is up to us to give Prescott better weapons with which to fight for more money from [the chancellor, Gordon] Brown," Sampson concludes. "In the meantime, the situation only gets worse."
Status Married, with two kids.
Lives King's Cross, north London.
Education Maidstone grammar school, Kent; Brasenose College, Oxford: degree in Classics, Masters in psychology and social policy; brief spell as junior dean of the college.
Career 1987-89: system probation officer, Probation Service; 1989-94: deputy director, Prison Reform Trust; 1994-97: deputy prisons ombudsman, Home Office; 1998-2003: chief executive, Rehabilitation of Addicted Prisoners Trust (Rapt); 2003: director, Shelter.
Interests "It's a sad and bitter fact that I am interested in all the sorts of things you'd expect. A mixture of low and high brow: cinema, football, music. Sleeping is an aspiration."
· Homes for All; Renewing our Communities, a special pullout in the centre pages of today's Society Guardian