Peter Youngman, who has died aged 93, belonged to the pioneer generation of UK landscape architects. They saw 20th-century development wrecking our landscape, and viewed the postwar Town and Country Planning Act and the New Towns Act as an opportunity to create new harmonies. With Sir Geoffrey Jellicoe, Dame Sylvia Crowe and Brenda Colvin, Youngman used a compositional approach, derived from garden design, to reconcile major new developments, such as Cumbernauld New Town and Milton Keynes, with the creation of a new landscape.
Youngman was born in Leeds, but the family moved to Hartlepool when he was three. His grandfather's farm had failed in the agricultural depression, and his father was a bank manager. Peter was given his own plot in what he described as the family's dull utilitarian garden.
He was educated at Cambridge University, where he read history. Not attracted to the usual career paths, he paid a firm of garden contractors £50 to be taken on as an apprentice for a year, laying crazy paving, building suburban gardens and being mocked for his university manners. Realising that design was his interest, in 1935 he became an articled pupil with George Dillistone, a garden designer, then vice president of the Institute of Landscape Architects (now the Landscape Institute). Youngman's next job was with Thomas Adams, a planner who had returned to Britain after seven years as director of the New York Regional Plan. Through Adams, he met the leaders of the planning profession, including Raymond Unwin and Patrick Abercrombie.
Youngman served first with the medical corps and then in the infantry during the second world war and had postings to Egypt, Palestine, Italy and Austria. In 1945, Jellicoe advised "there is a great future for landscape architects" and passed him private commissions. This led to work on the 1951 Festival of Britain landscape and on the 1956 masterplan for Cumbernauld New Town - designing the forest which helps protect this windswept site from North Atlantic gales. He gained a lecturing post at the Bartlett School of Architecture, University College London, where he became a visiting professor, retiring in 1978. He was awarded a CBE in 1983.
In the 1960s, his career blossomed. He was president of the Institute of Landscape Architects from 1961 to 1963 and undertook international commissions with the firms of Shankland Cox, Llewelyn Davies, and Colin Buchanan and partners. He recalled: "What a spectacular range of landscapes these travels encompassed: deserts, with camels and Bedouin flocks and sandstorms; coconut and orange groves, tea plantations, vineyards, lavender fields and aromatic maquis ... and what an architectural range too: the monuments of Washington and the skyscrapers of New York; the acropolis of Athens; the mosques, great maidan and bazaar of Isfahan."
With Richard Llewelyn-Davies, Youngman designed the masterplan for Milton Keynes in the 1960s. It would be a much harsher place without Youngman's input. An American grid of horizontal and vertical distributor roads had been proposed. Youngman walked the site, appreciated its gentle undulations and persuaded the planning team to convert the rectilinear grid into a curvaceous mesh, flowing with the landscape. He also argued, successfully, for a town forest to absorb the highways and create a framework for housing and recreational areas.
Youngman also worked on major infrastructure projects. As landscape consultant to Gatwick airport and Sizewell nuclear power station, he used ecological planting and compositional principles drawn from 18th-century landscape parks to weld new structures into old landscapes. The same principles were used for his delightful home in Kings Langley, Hertfordshire.
Youngman was able to combine consultancy with teaching architects at the Bartlett and landscape architects at the Thames Polytechnic (now the University of Greenwich). His critical approach was masterly and practical. While Jellicoe would comment on the meaning and significance of design drawings, Youngman's concern was with the details: "Where would I enter the site? What would I see on turning that corner?"
An extremely rational and kindly man, Peter is survived by his wife, Noreen, and two sons.
· Peter Youngman, landscape architect, born July 11 1911; died May 23 2005