The resignation, which insiders say has been the "only amicable stepdown at this company", was believed to be because Toad needed to save costs. Mr Cassey earns pounds 51,620 a year plus a car and benefits. He is on six months' notice and has no options. "The board was too top heavy," said insiders.
The parting follows the resignation of Charles Parker, chief executive, in February following "irreconcilable differences of style" after only 27 days in the job. In March, Kevin Turner, managing director, and Iain Brown, who ran the international side, left as part of a central overhead review promised by Kevin Gray, chief executive.
Mr Evans, who is Toad's non-executive chairman, said he wanted a more hands-on role and would run the research business himself.
"I've entrusted this company to other people and it hasn't worked out. It's my penance. I'll do the technical side myself - I'm not a bad scientist." However, analysts said the cuts showed Toad was still under financial pressure. In February the group said sales had fallen "substantially below budget".
But Mr Evans remained ambitious: "I plan to restructure Toad. I want it to be the world's leading car security company."
The group will launch an advanced immobiliser this week and there are rumours of a string of acquisitions and deals over the next few weeks, including a car security contract with a US group which could be worth pounds 50m in sales.
Mr Evans is also expected to announce a range of new research technologies outside the car security field in aerospace, telecoms and satellite via partnerships with technology companies. Mr Cassey is likely to advise Mr Evans on these projects.