BDP breathes fresh life into Mayfair’s historic Grosvenor Square

Grosvenor Square has been transformed by a £25 million redesign that turns London's second-largest public square into a woodland-style garden built to soak up storm water.

The scheme won a 2020 design competition for the landscape architect Tonkin Liu and was delivered by BDP for the Grosvenor estate, timed for the square's 300th anniversary. Work finished in July 2026. Planting was led by the late Professor Nigel Dunnett.

The central lawn survives, now ringed by shrubs, perennials and two ponds beneath the square's mature plane trees. More than 40 new trees, 70,000 plants and 82,000 bulbs have gone in, expanding the planted area from about 142 sq m to over 8,000 sq m.

Rather than burying tanks and pipes, the team set out to show Westminster Council that natural drainage could cope with a one-in-100-year storm plus an allowance for climate change, around 1.4 million litres of water across the 2.5-hectare site.

Decades of compaction were undone by forcing high-pressure air into the soil at more than 30,000 points. Biochar and a seaweed-based feed were added, and a new layer of topsoil laid by hand. Paths use a permeable cellular base designed to spread loads away from tree roots.

Source: RIBA Journal, 29 October 2026