Bell has a small equity stake in Mischief but Kaye's outfit will be run independently of Shine. Bell said: 'One of our philosophies is helping our staff to realise their ambitions and I am happy for Mitch.
'It was never our intention to grow Shine indefinitely and we are approaching our optimum size.'
Mischief is also already working for Channel 4 on an undisclosed project, Grant Bovey-owned investment property company Imagine Homes, and OTC cash payment firm PayPoint.
Kaye said he wanted Mischief, which offers consumer and some corporate PR, to be 'the most straight-talking agency in the industry'.
Thirty-year-old Kaye started his PR career as a Sky Sports publicist. He then spent two years at Shine before leaving to go travelling.
He subsequently worked at MacLaurin Communications and Geronimo Communications, before returning to Shine two and a half years ago as an associate director. He was promoted to a board director role 18 months ago.
Mischief has four other staff, the most senior being account director Jenny Lomas, who has joined after a brief spell at Consolidated Communications.