Most organisations / companies will have something in their policies and procedures about this, and I imagine that it could easily count as "gross misconduct". The firm will have their own procedures to go through, there will probably be some form of investigation followed by disciplinary action or sacking if it is found to be true.
I find it hard to think of circumstances where any employment tribunal would rule against a company who fire an employee for making racist remarks, unless maybe he suffers from Tourette's syndrome!
I can't say exactly what the law says about such issues, however your mate would probably have signed a contract of employment, and in doing so he signed to abide by the terms and conditions of employment, and it is almost certain that his terms and conditions would have included something saying he should not behave like this, or he could face action of some kind. He has therefore broken his contract in a serious way and that is probably grounds enough to have him sacked.
Edit: Was about to say that he should speak to his union or ACAS about this, but credit to Jake, he has already mentioned this.