Mace is main contractor on the £2bn scheme where prices for the 24 “principal residences” start at £35m.

Construction began in 2020 with full completion anticipated in Spring 2026. The team has included PJ Carey who have been responsible for the creation of the basement substructure and superstructure.

The topping out was marked by the final steel rafter, one of 79 at roof level, being put into place on the top of the nine-storey main apartment building.

With the building’s structure and basement now fully completed the next phases of construction include the finishing of the shell and core works and services and the installation and crafting of the Portland stone façades of the scheme.

Designers, specialist craftspeople and artisans from countries including Britain, Italy, France and America will create the classical architectural details of the façades and interiors.

Features will include porticoed entrances, 648 timber windows, each handcrafted by English window makers Mumford & Wood, 21 sculptural balconies, colonnades and a tiered façade to the uppermost floors providing pavilions with high ceilings opening onto private rooftop terraces.

Craftspeople will also be finishing the internal fit-out of the handcrafted interiors, including a rotunda featuring a ceiling with hand-painted frescos, a grand reception room with a double height ceiling and 18ft (5.5m) high French windows overlooking the garden and a Crystal Gallery, created from over 1,264 hand-set, cast glass pieces.

Developer John Caudwell said: “The topping out marks the completion of the structure and basement of 1 Mayfair and underlines the advanced stage of the project’s construction.

“1 Mayfair will deliver a legacy for London in the form of a landmark residential scheme that is timeless in terms of its architecture, design and build quality, setting a benchmark for London living and luxury design for centuries to come.”