In 1961, his firm, Grenfell Baines and Hargreaves, was reconstituted as Building Design Partnership, bringing together architects, engineers, landscape architects, interior designers, cost consultants and other specialists.
By the early 1970s BDP had more than 700 staff and spread across England and into Scotland and Northern Ireland, with several overseas ventures in the Middle East, America and Portugal. The firm won a stream of contracts for large public-sector projects, often hospitals and universities. The firm switched focus to private sector shopping development in the 1980s.
Among its gems were the modernist Halifax Building Society headquarters and the Millburngate shopping centre in Durham.
On his retirement in 1974 Grenfell Baines began another career as professor in architecture at Sheffield University. Married twice, with four children, he was knighted in 1978.