"What we've ended up with has the feel of a gentleman's home. It's very us," says Andrew.
They now have an open-plan kitchen-diner/office, a living room, a master bedroom suite with dressing room, a second bathroom and a WC. It is a happy mix of cosy homeliness with interesting textures, within a period property that is also a clean, modern space. Nowhere is this more obvious than in that kitchen-diner/ office at the back of the house.
"The original kitchen and living area (previously in the middle of the house) had no natural light so you had no idea whether it was sunny or raining outside," says Mark.
By knocking down walls and bringing the originally tiered garden down to ground level, they created a light-drenched area that blends outside and in, while producing an uninterrupted view that runs through almost half of the apartment. And the huge amount of natural light gave the couple the chance to play around with intense paint colours without making the flat appear smaller or darker.
"I've found from working with clients that people can be afraid of colour, but dark colours don't darken rooms as much as you might think - they actually just give an extra dimension," says Andrew.
"Definitely Farrow & Ball's Railings," the deep grey they used to give the sitting room a cosy feel. "As soon as the paint was on, that room came together." Andrew also loves Farrow & Ball's Arsenic Green for the bathroom, a shade that fuses the room's two influences - art deco elegance and classic Victoriana.
Every inch of space is put to good use, and while Mark's minimalist dreams never quite came to fruition, the flat is an inspiring new place.
* See Andrew Lock's work at andrewlockdesign.com.
* The couple's architect was Martins Camisuli (martinscamisuli.co.uk).
Photography: Jake Fitzjones
Styling: Shani Zion
* The full version of this article appears in the July issue of Livingetc, out now.