If management suspected s/he had attended work whilst under the influence of alcohol, then they should have informed the police, who may then establish reasonable cause and require a specimen of breath to establish if s/he was in fact under the influence.
Letting him/her work until 1100 before suspending him/her to my mind means they haven't got a leg to stand on. If they thought s/he was under the influence then they should have pulled him/her immediately or got the police to attend and determine if they could require a breath sample.
Management cannot require you to take a breath test, only a police officer in uniform can do so.
The Railways and Transport Safety Act has been well published and as a controller I am well aware of the legal requirements regarding alcohol and work, and I've no doubt that this controller was also aware, my guess is s/he was fine why else would management allow hime/her to continue working?