Kevin McCloud looks at the transformation of a derelict mill cottage in Northumberland into a contemporary family home, the longest-running project ever featured on the programme. Stefan Lepkowski and Annia Shabowska began work in 2006, and their ambitious plans involved restoring the Georgian building, reconstructing a watermill and adding a steel-and-glass atrium, but their budget of £250,000 was completely inadequate.

Paul and Penny are tearing down their million pound home in south London to build a contemporary mansion. But the challenge of building a complex home soon starts to bite.

Kevin follows the progress being made as Tim and Philomena O'Donovan, convert a lifeboat station in Tenby, Pembrokeshire, into a contemporary home.

Kevin McCloud follows the conversion of a large, Grade II-listed timber-framed barn in Essex into a family home and work-space by artists Freddie Robbins and Ben Coode-Adams. Their plans involve few interior walls to display their collection of toys, but at seven times the size of an average three-bedroom house, the transformation of the 500-year-old building proves extremely challenging.

Kevin McCloud meets estate manager Ed Waghorn and his wife Rowena, a couple living an almost self-sufficient life with their four children on a smallholding in Herefordshire. They have been constructing a timber-framed house using recycled materials, wood from nearby forests and stone from around the site, but as construction becomes a way of life for Ed they seem to have lost sight of their goal.

Ever since he was a child, stonemason Adam Purchase has loved the old silver mine engine houses that characterise Cornwall's landscape. When he and his partner Nicola Brennan chanced upon a dilapidated Grade II listed engine house with planning permission to turn into a home, it was a dream come true. But converting this important historic ruin into a place to live was never going to be easy. The building itself was little more than a shell, with crumbling plant-infested walls and no roof, windows or floors: a challenge for even the most experienced builders like Adam. Meanwhile the banks refuse to lend them more than £100k, which Adam and Nicola both know is barely enough to get them through. Still, driven by their passion for old buildings, Nicola agrees to support Adam while he takes a year off work to complete the project.

Claire and Ian try to build a home big enough for a disco on a small plot at the end of a London mews. But as angry locals begin to object to their plans, things start to go awry.

Running out of money is always a grim prospect for anyone attempting their own Grand Design. Perhaps no one has come closer than Robert and Milla Gaukroger. When Kevin last saw them a year ago, they were camping out in the incomplete shell of their ambitious Lake District home with their two children. With hundreds of thousands of pounds of work still to do, the bank was threatening to foreclose on the mortgage.

Kevin returns to the Weald of Kent and one of the most innovative houses ever featured on `Grand Designs', a highly experimental arch-shaped home built from clay tiles.

Kevin revisits Denise and Bruno Del Tufo who six years ago set about transforming a concrete water tower in their back garden into an avant-garde contemporary home.

Kevin McCloud revisits Alan and Judith Dawson in west Cumbria, where they began constructing a prefabricated home in 2009. They employed a method of building that should have allowed them to assemble the home in just 15 days on a budget of £300,000, and the presenter returns to find out whether they were successful.

Kevin McCloud revisits a couple who took on the task of constructing a sustainable house in the Kent countryside. Mimi da Costa managed the project despite a lack of experience, while her husband worked, and intended to have it completed in 16 weeks. But as the build threatened to drag on for months it became unclear whether their home would succeed in blending in and providing them with a greener lifestyle.