Task delegation presents one of the business process security leitmotifs. It defines a mechanism that bridges the gap between workflow and access control systems. Delegation completion and authorisation enforcement are specified under specific constraints so-called events. In this article, we aim to reason about delegation events to model task delegation and to specify delegation policies using a logical framework. To that end, we propose an event-based task delegation model to control the delegation execution. We then identify relevant events responsible for the dynamic enforcement of delegation policies. Further, we define a task-oriented access control model to specify delegation constraints into authorisation policies. Finally, we propose a technique to automate the delegation policies integration. Using event calculus, we develop a reasoning tool to control the delegation execution and to increase the compliance of all delegation changes in the existing policy of the workflow.