Florence Olajide takes to the road in September. She will say farewell to the children and colleagues she’s worked with for six years. From then on, the people she encounters will be nervous, maybe even scared, of her. Yet they will have to be won over, and sometimes persuaded to change their ways. She will have to analyse their work and write about it at home or in a hotel bedroom. Her boss will be an affable Scotsman, but he’ll be too busy for routine chats.

It was an advertisement in a January edition of The TES that persuaded Ms Olajide to change her life so drastically at the age of 40 and stop being a headteacher. On offer was the first chance in years to become one of the elite band of Her Majesty’s Inspectors.

Currently head of Crawford primary in the London borough of Southwark, Ms Olajide says she will miss her school. “As an HMI, every time I walk into a school I will be a stranger. And there will be a distance, a natural barrier.” But the Nigerian-trained teacher says her new role is a huge learning opportunity. “The advertisement just jumped out at me. I thought, ‘I can do that’.”

A thousand people thought likewise, but only 49 emerged successful from the rigorous selection process run by Ofsted, which employs HMIs. More than a third of these are serving headteachers, primary and secondary, and the rest come from a range of backgrounds, including further education and local authorities. Nearly two-thirds of the new recruits are women.

Deana Holdaway is one of them. For the past 10 years she has been head of Highfields, a large primary school in the West Midlands. “The only thing I am not looking forward to is leaving the children behind,” she says. “I can see the uncertainty in their eyes, and one little girl said to me, ‘You know, you don’t really have to go’.”

Yet Ms Holdaway believes she does. Since she trained as a teacher in Edinburgh, the 47-year-old has been driven by a desire “to make a difference”. “Being part of HMI is going to offer huge breadth of opportunity. I will be seeing the whole rich tapestry, whereas I can only see a little corner at present.” She respects HMIs for their high regard for children’s learning. They have always recognised that schools should offer “first-hand experiential learning in lessons that are memorable and meaningful”. They appreciate the importance of the joy of learning, she says. For her, the inspectorate, which was founded in 1839, has a history of being an inspirational force.

This sense of tradition is shared by Ms Holdaway’s new boss, David Bell, the chief inspector. “We have had to change the way we do business,” he says, “but I would be anxious if we ever lost sight of the strong thread of tradition we’ve had since 1839. It helps to generate a sense of pride in the organisation.”

Yet that thread had been fraying, despite the inspection explosion ushered in by Ofsted in 1992. Almost 50,000 schools have been visited since then, but the work has largely been handled by the 10,000 inspectors recruited by outside firms on contract to Ofsted. The tiny group of HMIs became increasingly involved in training and monitoring this army of accredited assessors. Some took early retirement, others left at 65. Numbers slumped to 175 and no new HMIs were recruited for years.

Mr Bell says he “doesn’t entirely know” why this was allowed to happen, but suggests a debate took place within Ofsted as to whether it needed its own permanent “field force” of inspectors any more. Clearly he believes it does, and authorised the recruitment drive soon after his own appointment last May.

The new HMIs, who bring the total number to 250, are a diverse bunch, he says, but all should have that “particular kind of expertise” that earns the respect of heads such as Deana Holdaway. In return, they get salaries of up to pound;56,000, a mentor, and an induction year in which to learn the skills of inspection. They also get computers installed at home with broadband access to the Ofsted network.

Mr Bell, who interviewed many of the recruits and is writing to them all, is keen to make sure they feel looked after. He talks of providing opportunities to meet colleagues and of professional development. While they will be attached to one of Ofsted’s seven divisions - such as primary, secondary, school improvement, and further education - they will work for at least one other division as well. “Nobody can know everything, but people expect an HMI to have a reasonably broad overview of education.”

They need to be able to go into an institution and make an impact quickly, he says. “The very best inspectors can combine excellent interpersonal skills with sharp judgment and strong professional knowledge.”

In the old days, a new inspector would be expected to move house to escape the influence of friends and colleagues - and to do so again every five years or so. While this is no longer required, says Mr Bell, “we have been very honest with folks, pointing out that this job might be unlike anything they’ve ever done previously. They are based at home. They work in small teams, and sometimes on their own. They will be travelling around, one day visiting a school in one part of the country, then, later in the week, for a different exercise, visiting somewhere else.”

Florence Olajide, for one, is looking forward to the travelling. “As a head you are pretty stuck in your own school,” she says. “You can get out, but every time you do you feel guilty that you are not there.”

Report writing is a large part of the job. An HMI, depending on his or her division, might write about the impact of the numeracy strategy, about prison education, about the performance of a local authority, about whether a school should go into special measures, or about issues such as bullying and ethnic minority achievement.

One recruit for whom some of this will not be entirely new is Bradley Simmons. A former head, he has spent the past two years working as an inspector for CEA, the private firm that runs school improvement services in the north London borough of Islington. He has a passion for seeing children succeed and is looking forward to joining “an organisation whose prime purpose is to defend the rights of learners”. He says: “HMI, throughout its history, has always been engaged with making sure learners get a fair deal, and that appeals to me.”

Mr Simmons, 42, is eager to work to David Bell’s agenda. “He has moved Ofsted on. The focus is now very much on engaging learners in the classroom rather than, for example, on teaching skills that might make no difference.”

Deana Holdaway agrees. “The role now is more about engaging with schools and inviting them to offer their opinion of themselves. It is more of a conversation, a dual approach rather than duelling,” she says.

“But it is still rigorous. Once you know what excellence looks like and how to achieve it; once you see the joy that young people can have in learning, then when you go into other schools that may be fighting all sorts of difficulties, you can offer hope.”

The aim of the new recruits is best summed up by Miriam Rosen, an HMI with 12 years’ experience who is now head of Ofsted’s new subjects and quality assurance division, known as Squad. “We try to do good as we go.”