Malcolm Roberts, 58, was found collapsed at the wheel of his car in the car park of council offices in Addlestone, near Chertsey, on Friday night.
The singer was best known for his sixties hits Time Alone Will Tell and May I Have the Next Dream With You.
His recording manager David Landau said on Saturday: "He was on the road in his car and pulled over to the side when he began to feel unwell.
"
He was a great singer, a true professional and a knock-out guy
"
Lee Stevens, BBC record presenter
"He apparently had a massive heart attack."
Surrey Police said they had been called to the scene by the ambulance service but were not treating the death as suspicious.
BBC record presenter Lee Stevens, a close friend for many years, said: "He was a great singer, a true professional and a knock-out guy."
Roberts, who was born in Manchester in 1944, had various roles on stage and screen before starting his chart career in 1967.
London musicals
He spent 14 weeks in the charts in 1968 but failed to find success with a potential Eurovision song in 1991.
In 1985 he represented Luxembourg, as part of a group that also included British singers Diane Solomon and Irene Sheer, with the song "Children Kinder Enfants".
He continued to sing and perform, appearing in musicals in London, and released his last album, The Essential Malcolm Roberts, in 2000.
He leaves a young son from a former marriage and a girlfriend, Susie.