It was transformed by architects Ian Hogarth and Claire Farrow who purchased it for £120,000 in 2007.
After converting it they rented it out for £875 a month but it is now up for sale for £225,000 - or £1,991 per square foot.
The front door of the property opens into the kitchenette which has built-in units, a fridge, a sink, a hotplate and a microwave combination oven.
Opposite this, separated by a sliding glass door, is a small wet room-style bathroom complete with toilet, sink and shower.
The rest of the room is a multifunctional 9ft 2in by 7ft 3in living space which acts as living room and bedroom.
Along one wall is a sofa with a double bed that pulls down from the wall above.
Mrs Farrow, 49, said: "When we bought it the walls were sticky and covered in grease. But these tiny, tight spaces really excite me because I know Ian can work wonders with them.
"Housing is desperately needed in London, but just because it is small doesn't mean it can't be luxurious."
Mr Hogarth, 62, said: "It's less than a third of the size of the national minimum new-build space standards but at some point someone had started living in it so when we bought it, its right to be used as a residence had already been established.
"But we had to make it user-friendly and employ ways of making it seem far more spacious than it really is.
"Whatever we are designing, especially in London, we are always up against the problem of space.
"This is the smallest space I have ever had to work in but it's the same principle I apply to larger projects - maximise every last inch.
"My most important rule is make everything work at least twice. It's a waste to give a space just one function no matter how big your house is."
The world's most incredible penthouse suites
The world's most incredible penthouse suites
One of the most exclusive and luxurious hotel suites in Rome, the Roman Penthouse takes up 560sqm of space, the entire eighth floor of the hotel. The stunning suite provides 360-degree panoramic views over the city's landmarks and is decorated with exquisite Italian detailing including Murano glass chandeliers. Guests can enjoy three bedrooms, four bathrooms, gorgeous outdoor terraces, a dedicated concierge, private chef, private barman and limo service. From €14,000 (£12,240) per night.
The romantic Bacchus Suite boasts approximately 150sqm in total, with its most beautiful features including a round copper hot tub and a large rotating bed which extends onto a furnished conservatory with a freestanding fireplace and a private exterior terrace from which to marvel at the panoramic views of Porto and the River Douro. Guests can also take in the views from floor-to-ceiling sliding doors and make the most of the excellent open-plan space that features an office, dressing room, lounge area and two plasma TVs. From £855 per night.
The 250sqm Royal Armleder Suite at Le Richemond, Dorchester Collection’s luxury property on Lake Geneva, combines a Premium Lake View Room, a Junior Suite Executive and a Presidential Suite. This splendid suite features a private hammam, a spacious living room and a dining room, as well as two private terraces. Located on the seventh floor, its terrace is one of the largest in Geneva with a 360-degree view overlooking Lake Geneva, the Old Town of Geneva and the striking backdrop of Mont Blanc and the Alps. From CHF 11,215 (£8,902) per night.
Corinthia Hotel London's Royal Penthouse is one of the largest two-bedroom luxury hotel residences in London. Overlooking the River Thames, it offers 180-degree views of the city from its sweeping terrace complete with loungers and a fire pit. Set over two storeys, the magnificent suite offers an imposing entrance hall, a panoramic living room and a high-tech study. There is even a private butler's kitchen and private wine cellar. Guests have access to a grand staircase and private lift taking them to the grand bedrooms with dressing rooms and marble bathrooms. From £22,000 per night.
Located on the 40th floor of this luxury hotel in Barcelona, The Royal Penthouse offers maximum privacy, independence and exquisite service. Guests can enjoy two bedroom suites, a spacious lounge with terrace, kitchen and a private gym with a personal trainer available. The interiors were designed with exclusive living and powerful architecture in mind, and some of its finest features include walk-in wardrobes and direct access to the hotel spa. From €14,000 (£12,240) per night.
Hotel Principe di Savoia has taken luxury to the next level with its elegant Presidential Suite, the only suite in Milan with its own pool. Its guests include some of the most acclaimed names, from royals such as Queen Elizabeth II, to film stars like George Clooney and Woody Allen. The suite includes a 100sqm Pompeian-style private spa where guests can unwind in the in-suite pool surrounded by frescoed walls and vaulted ceilings. This opulent spa incorporates a whirlpool, sauna and Turkish bath. Suite guests can expect gold, wood and velvet touches, along with the three bedrooms filled with art and antiques, and elegant entertaining spaces. From €17,000 (£14,800) per night.
Looking out over the majestic Furka Mountain Pass, this contemporary split-level Swiss chalet is twice the size of any other suite in The Chedi Andermatt, accommodating up to eight guests in three luxurious bedrooms and three bathrooms. Furka Suite guests can take advantage of the unique Ski Butler service, where professionals disclose insider secrets for finding the perfect powder. The suite's state-of-the-art facilities include HD IPTV TVs in all bedrooms and the living room, in-room iPad control, Bose surround sound system and a fully-equipped kitchen. The bathrooms offer a personal spa with steam bath, Jacuzzi and sauna, a built-in fireplace and a private wine cabinet. From £12,000 per night.
Boasting two regulation-sized bowling lanes, complete with shoes and a selection of balls, this retro-chic suite in Las Vegas is ideal for those who like 24-hour entertainment. The suite accommodates up to six guests across one king and two queen bedrooms, offering 4,500 square feet of space including a vast lounge with theatre-sized TV, a full bar and a pool table. Another perk of staying in the Kingpin Suite is VIP access to Ghostbar and Moon bar at The Palms. From £5,820 per night.
My Gstaad Chalet is the largest penthouse suite in the Swiss Alps, measuring 400sqm. It offers views of the Wispile Mountain and is accessed privately through its own secluded entrance. The chalet features four spacious bedrooms, each with their own black granite en-suite bathroom, dressing room, bar and kitchen corner, private dining area, and a 24-hour private butler. Complete with a private spa, which includes a sauna, hammam, Jacuzzi, tropical shower, treatment room and fitness room, the suite even offers its guests specially monogrammed bathrobes. Price available upon request.
Nestled in Hotel Cala di Volpe's tower and reaching a whole new level of elegance and splendour is the Penthouse Suite, by far the most magnificent in Costa Smeralda. Incredibly spacious and bathed in natural light, the 500sqm suite provides three bedrooms and three bathrooms, along with a wonderful private rooftop terrace featuring a large swimming pool, solarium and dining area. The suite boasts spectacular views of the island and dramatic coastline, while offering typically Mediterranean interiors and décor. Guests can relax in two spacious living rooms and have access to their very own wine cellar, private gym and steam room. From £28,277 per night.