Former minister Mal Brough, who this month quit the frontbench, has announced he will not contest the election.

Brough initially stood aside as special minister of state and then resigned from the frontbench because of the police investigation into his role in the James Ashby-Peter Slipper affair.

Allegations were made against former speaker Peter Slipper by Slipper’s staffer James Ashby. Police are investigating whether Brough illegally procured copies of Slipper’s official diary from Ashby.

Brough’s brief statement gave no reason for his decision. His spokeswoman said he wanted to focus on his family.

Brough was a senior minister in the Howard government. He lost his seat of Longman at the 2007 election. In 2013 he won Slipper’s seat of Fisher. In his statement he thanked the people of Fisher and the Fisher Liberal National Party membership.

Brough has repeatedly denied any wrongdoing in the Ashby affair.

He was one of Turnbull’s strong supporters in the leadership push. Turnbull’s critics said he should not have been appointed to the ministry in the first place, given the unresolved issue hanging over him.

Shadow Attorney-General Mark Dreyfus said Brough’s decision was not the end of the saga for the Turnbull government.

Dreyfus said Industry Minister Christopher Pyne and Assistant Innovation Minister Wyatt Roy had their fingerprints all over the Ashby affair “and they’re yet to give a full explanation. Their stories just don’t add up. Now Mal Brough has made his announcement today, it’s time for them to come clean.”