The GMB pair grilled Mark about whether he would change his mind about backing Theresa May's Brexit deal.
Mark insisted he wouldn't change his vote until Theresa made significant changes to her plans, and it didn't take long for things to get heated.
As Kate asked him a question while he was answering Susanna's, Mark panicked and replied: "I can't answer three questions at the same time."
Susanna frostily replied: "You aren't answering three questions at the same time, you were answering mine and then Kate asked you one."
Mark continued with his answers, but Susanna couldn't resist getting a jibe in.
She said: "You said you served in the army and you could cope under pressure, but you broke under the pressure of answering two questions."
Mark hit back: "I didn't break."
More to follow…