MATS Pt. 1 also says:
Section 1, Chapter 1, Paragraph 1.2.
The Manual of Air Traffic Services contains instructions and guidance for controllers providing Air Traffic Services to cater for both routine and many emergency situations.
However, nothing in this manual prevents controllers from using their own discretion and initiative in response to unusual circumstances, which may not be covered by the procedures herein.
If I was in control and there was a TCAS domino effect, I very much doubt I'd sit and watch the show unfold. Although it does depend on the specific scenario.