Along with Nick Hewer, Margaret Mountford is Sir Alan’s most trusted adviser: they monitor the contestants’ tasks, ensure fair play and — crucially — brief him before flanking him at the boardroom showdowns. “It’s nice to get praise,” she says. “Over the years I’ve built up a good working relationship: he knows I’ll tell him what I think without worrying if he agrees or not. He doesn’t like ‘yes’ men.”

That working relationship spans nearly 25 years. What is Sir Alan like? He does not, she says, treat her like the television contestants. “He’s a very shrewd, clever man — so he’s interesting to work with. He doesn’t have small talk — he won’t ask about your holiday. But he’ll talk at length when he gets an idea.”

In the series Mountford, like Hewer, says little. She seems rather stern, a bit schoolmarmy. In reality she’s chatty, laughs a lot and her role is clearly central. “We have quite a long briefing session before the boardroom . . . on who did well, badly, our views . . . and he takes those into account. Sometimes we know who’s going out — it’s obvious. At other times it may be one of two — it depends on what he’s looking for, whether it’s someone good at sales, for instance, or a more managerial type of person. But someone whose sales technique he admires I’d probably never buy from. It’s horses for courses.”

Mountford, Sir Alan told her on air, “couldn’t sell a box of matches”. She had looked put out. “I thought it an unnecessary insult. He was right: he knows I don’t like selling. But I thought: bloody hell! Why would I want to? I’ve never thought of myself as a little matchgirl. I did remonstrate with him but that was all cut.”

Her contact with Sir Alan began when she was a corporate lawyer at Herbert Smith. “It was in the 1980s when Amstrad went public and the firm acted on the flotation, brought in by Kleinwort Benson. I was the senior assistant on the flotation. Corporate law appealed because of the buzz of the deals — there was always something new.” After that, she worked on several of his transactions; and then there was the Terry Venables dispute when Sugar owned Tottenham Hotspur. “

The court case that followed (Venables’ sacking) should never have happened, it should’ve been thrown out. I advised Alan he was entitled to sack Venables, and I was right. But it was horrible for him, the acrimony and personal hostility he suffered — being spat at as he went to court. Some fans, in my opinion, are little better than savages. It’s very tribal.”

But seven years ago, at 47 and nearing the peak of her earning capacity, she felt she’d had enough. “I just got fed up with it.” Not being married or having children, she could do something else. She ruled out becoming a lawyer in-house (“deathly”) and plumped instead for university: first for a full-time degree in ancient world studies at University College London, then a part-time MA in classics and now a PhD in papyrology. And she took on a clutch of non-executive directorships, including Georgica (bowling alleys, sports clubs) and Amstrad, of course — Sugar still consults her. She’s also a trustee of Corda, a heart disease charity, and chairs the governors of St Marylebone’s School for Girls, a church comprehensive.

Herbert Smith came after she had read law at Cambridge (switching from French and German): her father was a clergyman in Northern Ireland, where she grew up, so training for the Bar was not a financial option. “And I’ve not enough of the actress in me.” So she’s bemused to find herself a celebrity of sorts on a programme with up to 4.6 million viewers a week. “As a City lawyer you’re pretty faceless outside the clients, the accountants, those you deal with. Now, people come up to me in the street, they feel they know me. I was walking along and someone said: ‘That’s Alan Sugar’s woman’.” Nor is she a television fan; she has a set but never knows the programmes people are talking about.

Except this one, of course. “It has been great fun.” The programme’s climax can surprise — the lawyer Karen had come across as “rather smug and complacent” in the boardroom. That had probably rankled with Sir Alan, she says. And it can shock, even her and Hewer. “When he said, you’re fired, you’re a lightweight (to the Cambridge economist who got muddled at the till), yes, we do feel for them.” People did not always appreciate how tough it could be: “They’re confined in this hothouse environment for eight or nine weeks, no mobiles — just one phone call a week allowed. It’s a bit like being under house arrest.” In reality, she insists, Sir Alan is not as brutal as he seems — “gruff and blunt, but fair. People stay at Amstrad for years. He hates firing people.” As for whether she’d be a good contestant herself, she’s in no doubt. “I’d be absolutely dreadful. You have to be insane to go on that programme.”

The Apprentice: How to Get Hired not Fired, £7.99 BBC Books

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