Fraser Bond are the leading lettings and property management agents for Devonshire House - London W1J. Devonshire House is an office building opposite The Ritz London hotel and Green Park in Mayfair, London W1. The building sits above the Green Park tube station with entrance from Piccadilly. The current building was designed by Thomas Hastings and completed in 1926. It was named after the London Mansion of the Dukes of Devonshire that once stood on this site. - Size: 187,000 sq ft (17,400m2) - Roof terrace on the 3rd floor - 24h security - 6x18 person passenger lifts The nearest underground.