Barbara Henning, widow of Alan Henning, with Michael Haines, the brother of David Haines, the two British aid workers beheaded by Islamic militants, at the Perth Congregational Church prior to a memorial service for Haines. Photo: Danny Lawson/PA Wire

The families of two British hostages who were beheaded by Islamic militants have come together in a show of unity at a special service to celebrate the life of one of the murdered men.

Michael Haines called on people to join together and “find a single act of unity” in the wake of the barbaric killing of his brother, David Haines.

Father-of-two Mr Haines was taken hostage in Syria while working for international relief agency Acted in March last year.He had been been helping refugees in a camp near the Turkish border when he was snatched by Islamic State (IS) militants.

Tributes were paid to him a memorial service in Perth, which was also attended by the family of Alan Henning, who was also killed by IS.

His widow, Barbara, and two children travelled north to attend the service at Perth Congregational Church, which was described as a “service of thanksgiving and celebration for the life of David Haines”.

Mrs Henning and Michael Haines stood together and held hands outside the church before going in for the service, which was attended by more than 600 people.

In a joint letter published in the Guardian newspaper, they called on people to come together in a bid to defeat the terrorists.

“Together we have the power to defeat the most hateful acts,” they said.

“We condemn those who seek to drive us apart and spread hatred by attempting to place blame on Muslims and the Islamic faith for the actions of these terrorists,” the letter stated.

The pair said they have been overwhelmed by messages of support from around the world.

Born in Yorkshire, David Haines was brought up in the Perth area and attended the local academy before serving 12 years as an aircraft engineer with the RAF.

He later took up humanitarian work and assisted aid agencies in some of the world’s worst troublespots.

He was in Libya during its civil war in 2011, working as head of mission for Handicap International, which helps disabled people in poverty and conflict zones around the world.

Mr Haines has a teenage daughter, Bethany, from a previous marriage and a four-year-old daughter in Croatia with his widow, Dragana Prodanovic Haines.

Michael Haines said his brother’s death had broken the family’s hearts but they had been “overwhelmed” by messages of support from the British public and people all over the world.

As the service was a celebration of Mr Haines’ life, his family had encouraged people to come dressed in bright colours. One man in the congregation wore a co lourful yellow Hawaiian-style shirt and red tartan trousers, while Michael Haines wore a green and purple kilt teamed with a purple T-shirt and black leather waistcoat.

Bethany Haines arrived in a floral dress, clutching a single white rose.