More than 600 companies – most of whom are construction clients – are signed up to gay charity Stonewall’s Diversity Champions programme, which costs around £2,000 a year to join.

Chris Edwards, client manager at Stonewall and a former employee of the Commission for Architecture and the Built Environment, said: “I think there is some momentum growing and Arup being so public about joining sends a really strong signal.”

Presently, no construction firms make Stonewall’s workplace equality index of 100 leading employers, based on company equality policies and responses to a staff survey.

Arup plans to join the index making it likely to become the first construction firm to enter the top 100.

Alan Belfield, Arup Group Board Director and Diversity Champion, said: “We are now looking forward to contributing to Stonewall’s Workplace Equality Index which will enable us to measure our extensive and ongoing efforts to create an inclusive workplace – testing us against the best and challenging ourselves to foster a working environment that allows people to feel at ease, be themselves and reach their full potential.”

Kier’s building maintenance arm and Lend Lease are the only other construction companies that have committed to the scheme.

Other members include housing associations, local councils, Government departments, fire and health services and universities.