He and non-executive directors Lyndsey Cattermole and Anthony Clarke announced their resignations today (19 September), with plans to leave in less than two weeks.
It is understood all three resignations were entirely unexpected.
Non-executive directors Andrew Price, who was recently appointed to the board, and Michael McConnell remain.
The company expects to make additional appointments to the board prior to the departure of Boon, Cattermole and Clarke on 28 September.
The shuffle follows a number of high profile changes in the company, including UK commercial director Malcolm Lane-Ley's exit last month and interim chief executive Dave Allen taking over from Toby Marchant.