The Anglican and Catholic churches in England have joined forces to urge people to watch out for signs of modern day slavery at car washes and report their suspicions to the authorities.

An app to help members of the public identify signs of forced labour is being launched on Monday by the Clewer Initiative, the Church of England’s campaign against modern slavery, and the Santa Marta Group, the Catholic church’s anti-slavery project.

The Safe Car Wash app has the backing of key agencies, including the police and councils, and is part of a drive to tackle the exploitation of workers at some of Britain’s 18,000-plus hand car washes. Many are legitimate businesses, but some threaten workers and trap them in modern slavery.

The app will pinpoint the location of hand car washes using GPS. Users will be shown a series of indicators of modern slavery, such as whether workers have suitable protective clothing or whether they appear withdrawn.

Users can be directed to the Modern Slavery Helpline and data from the app will be anonymised and shared with the National Crime Agency and the Gangmasters and Labour Abuse Authority.

The archbishop of Canterbury, Justin Welby, said: “Over the last few years we have learned more about the evil of modern slavery and we have begun to understand how it is perpetrated in our communities in plain sight.”

The app provided help in tackling “this scourge which is damaging so many people’s lives”, he said.

Cardinal Vincent Nichols, the archbishop of Westminster, said: “As we learn … we will also become more aware of the presence of this evil scourge in other sectors in our neighbourhood.”

Kevin Hyland, the independent anti-slavery commissioner, said: “In addition to immeasurably improving the lives of victims of modern slavery being cruelly exploited in car washes today, [the app] also empowers a community to act.”

Clergy will also be asked to raise awareness of the campaign in sermons and Sunday school lessons and hold events to publicise the app.