If the banter was 'harmless' the only issue would involve wasting company time. However, if it was unlawful you could be disciplined and the sanction could even be sacking if the matter was racist, sexist or defamatory since employers have a duty of care to all employees and, their failure to deal with such incidents would open them the possibility of litigation in which the damages could be punitive.and costly. What should govern their decision should be to respond in a reasonable and proportionate
way under the circumstances.
In any case you should get representation and legal advice from your union, the citizens' advice bureau or some other source. Do any of your insurance policies offer legal protection?
Jock