Mr Whittle commented after Scottish Tory party leader, Douglas Ross made clear he believed Boris Johnson had broken the rules on social gatherings in place at the time and should go.
Mr Whittle said: “Given the Prime Minister’s admission he attended this event in the Downing Street gardens, it’s clear to me that he has broken the rules he was asking us all to follow.
“If it came to light that Nicola Sturgeon or any of her Ministers had done something like this I would have no hesitation in calling for their resignation, so it would be wrong of me not to say the same here just because Boris Johnson wears the same colour of party rosette as me.
“This isn’t a question of politicians being held to a higher standard, it’s about them sticking to the same rules as everyone else and ensuring those who work for them do the same.
“Boris Johnson has failed to do that and, perhaps worse, he’s damaged the credibility of his office at a time when the public need to have trust in their government to see them through the pandemic.
“He has admitted he did the wrong thing, now he needs to do the right thing and resign.”
Galloway and West Dumfries MSP Finlay Carson also believes the Prime Minister should resign tweeting yesterday (Wednesday): “I absolutely support Douglas Ross’s position, did yesterday and do today!”