The Conservative member for St Austell and Newquay apologised after accepting he had behaved "completely inappropriately".
He admitted to having a short affair with 26-year-old Sarah Bunt, his political aide.
Now Mrs Bunt's father in law, Phil Bunt, has accused the MP of hypocrisy, saying he stood on a platform of family values and his Christian faith.
He has resigned his position as deputy chairman of the Tory party association in St Austell and Newquay citing 'personal and ethical reasons'.
"He has let many people down and shown himself to be hypocritical when getting elected on the basis of his stated position as a family man and a Christian," Mr Bunt said.
Double, 49, has been married to wife Anne for 29 years and they have three sons.
Speaking to the Telegraph this week, he said: "I confessed to Anne last week. We are both committed Christians and we are both forgiving. I am incredibly grateful to my wife. She is an amazing woman. I doubly regret what I put her through. I love her more than ever."
She has previously stated she would not throw their 30 year marriage away over the incident.
