GLA and Vehicle & Operator Services Agency (VOSA) officers inspected nurseries and vehicles, and interviewed 130 English, Polish and Slovakian daffodil pickers supplied by gangmasters.
GLA chairman Paul Whitehouse said: "When a worker does not get a chance to work and owes mounting accommodation debts to the gangmaster they are in danger of exploitation. Debt bondage is a disgrace and I will not stand for it.
"If you suspect worker abuse, including workers in overcrowded housing, or see unfit minibuses used to transport them, tell us."
Officers found that on certain occasions:
- workers were transported on a plank of wood held up by breeze blocks in the back of a van;
- some workers had been charged £60 a week for accommodation and had not been given any work for three weeks;
- workers were required to surrender their passports to the gangmaster;
- the agricultural minimum wage was not paid;
- workers were charged excessively for accommodation - some charges were over £30 per week more than the legal requirement for minimum wage workers;
- workers did not receive holiday pay;
- workers were charged for personal protective equipment to carry out their jobs.
VOSA issued two prohibition notices on minibuses used to transport workers.