Sisu
https://www.gov.uk/employment-contracts-and-conditions/contract-terms
Having been on the wrong end of a tribunal decision, I can tell you it is that simple.
In a situation where it is not witnessed and one party denies the others version it is not as cut and dry as you would suggest. Anyone knows in all meetings between you and employer you need someone to accompany you into that meeting with your boss and the boss as well.
I've been in that situation more than once, if you go into a meeting alone with your boss, anything verbal is subject to denial and or interpretation.

