Anti-speed camera campaigner Paul Smith died last night aged 52.
The founder of the website SafeSpeed.org.uk is believed to have suffered a stroke or heart attack at his home in Fife, Scotland.
He had suffered two earlier heart attacks including one this summer.
Smith's work exposing failures of speed cameras had made him a respected and credible authority quoted frequently in national press.
Claire Armstrong, his partner of 22 years, said she planned to take over the running of the website.
She said he was talking on the phone when he “suddenly took some deeps breaths and stopped responding”.
“The thoughts from the doctors are that either he had a stroke or a vital artery became blocked,” she said.