“Being a woman can be an advantage in business. Typically it gets you noticed more,” she says with a smile. “And people remember you — hopefully for the right reasons.”

Then she bursts into infectious laughter. King, chief executive of Voca, the automated payments system previously called BACS, is nothing if not a compelling saleswoman.

Sitting in an air-conditioned meeting room below Voca’s rented London base in Cornhill, she looks every inch the City queen: 5ft 9in, brown Armani suit, bobbed hair, bright red lipstick.

And when she speaks, it comes in a rush, every phrase laden with purpose, whether it’s pitching her business or her home-life. Her husband, a former restaurateur, sold up his business a decade ago to stay at home and look after their kids and cook — that, she knows, makes her the envy of many businesswomen. “I’m not daft,” she nods.

But King, 48, formerly head of Reuters’ East Asian division, is more than just a designer-clad whirlwind. She made her name selling data systems to trading floors and is, by all accounts, a very serious executive, accustomed to cutting a swathe through male-dominated businesses.

All of which makes it intriguing to find her at Voca, the technology firm that provides a vital cog in Britain’s economic infrastructure — paying wages and running direct debits — but whose arcane wizardry tends to get minimal coverage.

Owned by Britain’s biggest banks, but now set on a newly independent course, Voca has long been a victim of its own success. You wouldn’t notice it unless something went wrong, and up to now it hasn’t.

“It’s the UK’s best-kept secret,” says King. She rattles through its hold on everything we do: 90% of UK salaries, 70% of household bills and the majority of state benefit and pension payments — all processed by Voca.

King has spent the past four years supervising an overhaul of the system’s infrastructure. Colleagues say the breadth of change cannot be exaggerated. “Every nut, bolt, and widget has been changed,” says Voca’s chief operating officer, Steve Grigg, another Reuters veteran.

That faster, more flexible system came on stream this summer, and Voca now has its eyes on opportunities elsewhere. Europe wants a common standard in payment systems — so we can pay bills electronically in any country — and consolidation is likely. Voca could provide the system of choice.

That might give the banks that own Voca a return on their investment. But they also want the chance to shop around if another system prevails.

So will they float Voca? It’s not on the agenda, says King, but it could happen eventually. “Owning this is not something banks need to do,” she says.

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