I'm no expert but I need to know a little for the business. In my experience you can pretty much sack anyone, as long as your contract and policies set out what is acceptable behaviour and what is not. However, I employ folk at just above the minimum wage who don't have agents and hence expensive lawyers to go through my contracts and ask to have clauses removed before they sign them. So in effect I can bring someone in for poor or unacceptable performance give verbal warnings followed by written warning, followed by the dunt. You have to be ruthless from the beginning though and make everything official following guidelines set out by ACAS.
If what is being suggested about Leitch is true I would hope the club dealt with it appropriately the first time through proper disciplinary procedures culminating in a written warning (which would allow the club to dismiss regardless of time-scales set out for how long it remains on file as it is a second offence of the same nature) as this is the minimum I would expect for bullying.
If McGhee wants to walk with him, I suppose he could then slap in a ET1 for constructive dismissal but it would be a very hard case to prove, as long as Leitch has been properly dealt with.
Then again it's a football club and as much as they want us to believe they exist in the real world, they don't.