There should be a company proceedure to follow and it is usually found in the employee handbook.
He should be interviewed in the presence of his witness and a company witness.
It depends on the severity of the allegation against him and notices of any action taken against him should be presented in written format. At every stage he should be given the opportunity to state his case.
All in all, he should at least be given a reason. This doesn't indicate well for the employer and would suggest that they not fully conversant with employment law.
You could contact ACAS
http://www.acas.org.uk