I always avoided Line management roles!
Mrs @BoldonLad was a line manager. Her technique for employees such as you describe, was, short reference, but, if a potential employer had the wit to make a telephone call, then.....
Secondly, she NEVER employed anyone unless she could speak to their former employer on the phone.
Seemed to work, only once in 30 years did she get a dud.
In my experience they just do it verbally over the phone.Does anyone know the figures on employers getting into trouble for writing negative things in a reference?