Up until recently, in these circumstances, the company would be guilty of Breach of Contract, with potentially very serious consequences, if they failed to follow their Disciplinary Procedure. However, a recent tribunal, which went to appeal and further appeal, has determined that if a company fails to follow a disciplinary procedure that is contractual (ie contained in the contract of employment), they won't be guilty of Breach of Contract - just guilty of failing to follow their own disciplinary procedure.
This is good news as the penalty is potentially less severe but, in an unfair dismissal claim, they could still find themselves having to pay out over £70k! This could literally put a small company out of business - but a Tribunal wouldn't be interested in that... just the facts of the case before them.
So, yes of course you must have a Disciplinary Policy and Procedure. But keep it as a separate employment policy - non contractual. It will still need to be followed during disciplinary proceedings, but you will be free to amend the procedure in line with the needs of your business, just as long as it follows ACAS guidelines as a minimum.
ALWAYS follow your company's procedures - to the letter! You could be heavily penalised if you don't.