Marianne Lumb gave up a place at a prestigious architecture school in London to peel potatoes at the Olde Stocks restaurant in Grimston, Leicestershire. Anyone who saw her asparagus crowns on MasterChef: The Professionals – they looked like classical order temples – knows she has an eye for form.

She packs her food with another prized ingredient, too, highly sought after by judge Michel Roux Jnr - “flavour”. Her first food memory is finishing off the mashed potato with loads of butter, salt and pepper, aged five. “I was a greedy child who ate everything – even spinach - maybe that’s why I grew so tall,” she says. At a little over 6ft she towers above Roux, though the camera angles rarely let this show.

Despite the occasional “crumble” under pressure and a penchant for undercooked meat, Lumb, 34, holds her own on the all-male BBC show. But there are moments when she feels excluded. “Daniel and Steve are good mates [with each other] and quite blokey so there are times when I feel left out. They like to wind me up but they’re lovely and after an experience like this we’ll be mates for life.”

One thing they all have in common is an obsessive nature and a will to win: “We’re all perfectionists,” she says. “One negative comment, even if 99 per cent is good, and we beat ourselves up about it.”

Lumb worked a spell in the Michelin-starred kitchen at Gravetye Manor in West Sussex ten years ago, but as the only chef among the three not currently working in a restaurant kitchen she admits that her presentation and attention to detail might not be as consistent as that of her fellow finalists. Her work, however, as a private caterer allows her to withstand the sort of grin-and-bear it interference with her food that “a cheffy chef just can’t handle”.

“I cook what people want to eat rather than what I’d choose to cook if I owned my own restaurant. Both Steve and Dan use sophisticated techniques and have an exquisite gentle touch but sometimes that’s too fiddly. I prefer to keep food closer to its original state.” She describes her food style as “stylish, eclectic and seasonal with a luxurious feel”. Her favourite cuisines include Italian and Thai and she adores the cosiness of La Fromagerie, a cheese shop in London’s Marylebone.

So how badly does she want to win tonight’s final?

“I’m already pretty successful and have a great client base [she cooks privately for high-profile celebrities and politicians, including Elton John and David Cameron, but refuses to reveal more details – perhaps a wise move given the furore over favourite biscuits last week]. But it would be fantastic and a great accolade to win. Equally, being the first woman in the top three is brilliant,” says Lumb.

Win or lose she will take away a great deal from the experience. “Other chefs work a lifetime to get praise from the Roux family. Michel was fantastic and very supportive. I think he’s fair but he could be really annoying when he said things like ‘It needs a bit more seasoning’ (she mimics his voice in coddling tones)”. Much of the praise she is hearing for the first time as the show is aired on TV this week.

Growing up in Long Clawson, where Stilton is made, Lumb would pick up cheaper “tastier” cuts of meat such as brisket and ham from her father’s butcher’s shop on the way home from school. Her mother would cook Julia Child’s boeuf bourguignon in the Aga, followed by chewy meringues.

Lumb shone in home economics classes at King Edward VII school in Melton Mowbray, foodie central in the Midlands and home to the famous pork pies, where she cooked blancmange, scones, and baked apples. She’s keen to get cooking firmly back on the school curriculum.

Winning tonight will help with her agenda. But the task in hand is a formidable one – cooking dinner for 30 chefs with more than 40 Michelin stars between them.

“At least they’ll understand what we’re going through and will have some sympathy. Besides I cook every meal like its going to the Queen or Michelin inspectors.” The proof will be, as they say, in the starter, main and pudding.

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