Speaking during the radio phone in on Wednesday morning (August 2), Sunak was quizzed over why Dorries had not spoken in the Commons for around a year.
Sunak came out swinging and referenced Dorries' slow march to resigning.
"I think people deserve to have an MP that represents them wherever they are," the prime minister said.
"It's just making sure that your MP is engaging with you representing you, whether that's speaking in Parliament or being present in their constituencies, through surgeries, answering your letters. That's the job of an MP and all MPs should be held to that standard."
He added: "At the moment people aren't being properly represented. We have a strong Conservative candidate there, Festus Akinbusoye, who has been doing a great job as Police and Crime Commissioner previously or currently and I think people there will see that we've got a fantastic candidate for them to represent and going forward."