Derek Walker: Architect whose greatest achievement was serving as the chief designer of Milton Keynes, the 'Forest City'

Walker represented a diverse and inclusive approach to architecture, with people at its core

Walker, centre, standing, in the early 1970s with the team that created Milton Keynes

Derek Walker, who has died aged 86, was best known as the chief designer of Milton Keynes. He was born in Lancashire in 1929 and was brought up and educated in Yorkshire; he possessed the combination of utopian romanticism and pragmatism embodied in both counties.

A chance encounter with Herbert Read in a York bookshop sparked an interest in architecture that was nurtured at Leeds University. This was followed by further studies in town planning in Philadelphia, which exposed him to the forward thinking and urbanism of postwar US. This amalgam of English and American sensibilities informed much of his design thinking; he was not afraid of commerce and car parks, but he also recognised the need for culture, social interaction and human scale.

He returned to the UK in 1960 and began an award-winning career in private practice in the north of England, which in 1969 brought him to the attention of Fred Lloyd Roche, Chief Executive of the Milton Keynes Development Corporation, who was looking to appoint a chief architect and planner.

At Milton Keynes, Walker developed the low-density masterplan set out by Llewelyn Davies, combining the restoration and extension of 11 villages with a "downtown" grid structure to produce 3,000 homes a year, linked by a radical, low-density, greened infrastructure. He was ahead of his time on now commonplace ideas on green issues and sustainability; a fifth of the city's area was allocated to open green space with a massive tree-planting programme; by 1973 2m trees had been planted, linked with 180 miles of "redways" – bridleways, cycle tracks and footpaths.

Walker's concept was of a "Forest City" greener than the surrounding countryside, which had been ravaged by Dutch elm disease and agricultural clearance. In addition to the landscaping, the defining features of the masterplan were the Central Milton Keynes and Central Area Housing grid squares, both of which could be seen as US-influenced planning concepts, which completed the overall planning matrix of landscape and infrastructure. The "downtown" central area was modern, reminiscent of Mies van der Rohe in style, and has been critically acclaimed; the main shopping centre was Grade II-listed in 2010.

Walker recruited the best talent he could find to his 200-strong team. No one was much over 40 and the young idealist novices soon became experts in industrial building systems, ecology, conservation, housing design and landscape; many, like Ed Jones and Jeremy Dixon, went on to form successful practices. Walker also brought in the best consultants to design individual buildings: Norman Foster, Henning Larsen, Edward Cullinan and Ralph Erskine were among many who helped to shape the architecture of Milton Keynes.

Behind Walker's often mischievous ring-leader persona was a serious, well-read mind and a steely determination, and he often talked of the hard work and nimble-footed bloody-mindedness needed to deliver such a large public scheme. He conceded that the initial utopian optimism was difficult to sustain, and after changes in political structure and funding he was clear that, in his words, "opportunistic political doctrines are not the right foundations for building for the future, and it is misguided to believe that private interests and market forces will look after our environment."

He was concerned about the gradual diminution of development control and design quality after he stepped down, but he took heart that Milton Keynes remained commercially and socially successful and that he had orchestrated the creation of a habitat that facilitated human development and growth with space to breathe in an environment to enjoy.

The ethos of the place and time was captured in the team photograph of the entire planning and architectural group photographed up a tree and in front of it, worthy of a '70s Pink Floyd album cover, as well as in the film adaptation of Lee Scriven's book 3 Curly Wurlys and 106 Roundabouts, which told the story of MK's development; both capture the love, affection and inspiration that everyone who came into contact with Derek Walker experienced.

While the achievement of MK is perhaps Walker's defining work, after leaving MKDC in 1976 he formed a successful international architectural practice, designing the Royal Hong Kong Jockey Club at Kowloon Park and the master plan for the new city of Jubail in Saudi Arabia, as well as an unbuilt joint proposal with Norman Foster for an extension to the Whitney Museum in New York, and, closer to home, the Royal Armouries in Leeds.

He sometimes expressed regret that his vision for Wonderworld in Northampton, developed with his close friend and client Iain Quicke, wasn't realised. It would have been a unique leisure-based development in the UK comparable in scale to the pioneering Disney parks, blurring boundaries between theme park and museum to create an educational challenge to the intellect and the imagination; it would have established the template that many museums and galleries have subsequently implemented as attractions. But he was never one to look back and of late had been involved in preparing the way for several large ecology-generated schemes in Sri Lanka and Malaysia, as well as monitoring the Royal College of Art's campus expansion in Battersea.

Walker's increasing appeal to a younger generation of architects amused him. He represented a diverse and inclusive approach to architecture, with people at its core, and he tackled the messy complexities of commercial and political reality head-on. But it also was a true reflection of his capabilities as both practitioner and teacher. As Professor of Architecture and Design at the Royal College of Art and visiting professor to a number of American universities such as UCLA and University of Pennsylvania, he taught and inspired a generation of younger architects now firmly established in architectural practice.

GRAHAM HAWORTH

Derek John Walker, architect and teacher: born Blackburn 15 June 1929; married firstly Jill Messenger (two sons), married secondly, thirdly Eve Happold; died 11 May 2015.