MATS 1 Section 1 Chapter 1 Page 1
"1 Introduction
1.1 Air Traffic Services within the UK are provided in accordance with the Air Navigation Order and Rules of the Air Regulations. Generally these are in line with the Standards and Recommended Practices of the International Civil Aviation Organisation.
1.2 The Manual of Air Traffic Services contains instructions and guidance to controllers providing Air Traffic Services. Nothing in this manual prevents controllers from using their own discretion and initiative in any particular circumstance. "
Nothing mentioned about confining discretion/initiative to collision avoidance.