Depends on his previous conduct and his length of service. If he has been there over a year and has not had issues before, he will probably get a written warning, inless he can demonstrate that his floor manager was behaving unreasonably.
If your partner stays calm and rises above any possible annoying input from his line manager, he should show himself to be the better person and that may have a big bearing on the outcome.
Best advice is to go to ACAS website and ring them for the legal position - they are a very good FREE mediator in issues like this.
http://www.acas.org.uk
Good luck, let us know what happens please!