It's warranties again...
My advice, if the fault is demonstrable, is to insist someone from the workshop comes out to the car and show them the fault - get them to see or feel it for themselves and accept that the fault exists, if at all possible. Then get the service department to use their judgement to tell you if it would be covered by warranty, and if not, explain why not.
It still find it astonishing that they can casually thow a potential £500 bill into the discussion if they "find nothing wrong", or can't find what's wrong, it's tantamount to blackmail. How you are supposed to commit to that without a crystal ball is beyond me.
In any case, four hours to diagnose a clicky steering column? Who's doing the work, Brian off the Magic Roundabout?
As Jocko says, take it somewhere else for a diagnosis first. I know you shouldn't have to, but unless the dealer is prepared the waive the diagnostic costs, it's a lot to commit to without any guarantee of a fix - in fact quite the reverse, you'll pay if they don't fix it!