OK, so I think that your starting point was 'if an employer uses an obsolete Disciplinary Procedure, does that nul the process'. To which I replied 'probably not.
You've now given a lot more about the case - your relative has been given a 1st Written Warning over an incident involving alleged misconduct for authorised absence. He thinks it is unfair.
On the face of what you reported I have to agree (yes, I've been involved in lots of these). However there are 2 sides to every story and I don't know what the other side had to say about it.
Rather than debate the pros and cons of the case, I'm going to point you to the ACAS Code of Conduct on discipline and grievance. It is here and you can download it:
http://www.acas.org.u...ia/pdf/l/p/CP01_1.pdf
It is not law that employers have to work exactly to it - but most employers who choose to write their own base theirs on the Code. It is also regarded as good employment practice in the (unlikely event in this case) of an case going to Employment Tribunal.
What you will in the Code are two things - how to run a decent disclinary interview and how to run the grievance procedure.
Your relative may elect to invoke the grievance procedure. Perhaps compare what it says in the old 1992 document about grievance - even 20-odd years ago this was good practice so it should be in there. If he does, take someone with him (was he told he could be accompanied at the DI? - he should have been - it is in the Code). Perhaps prepare a written notes beforehand on the main points to bring out at the meeting. The objective would be to get the Written Warning cancelled.