Mostly it’s fairly clear which side any given witness’s evidence supports, but once in a while there’s a witness who has relevant things to say,…
There is now a useful discussion of privilege, including waiver (see previous post), by the President of the EAT in Howes v Hinckley Bosworth BC
Employers can be careless about accidentally waiving privilege. If they mention the legal advice that they have received in their witness statement, they may have waived their legal professional privilege and given you the chance to demand to see the advice.