Introduce employment contracts and Job Descriptions for Members of Parliament.

When other public servants lie, submit false or incorrect expenses, or working in a second job when they should be at their workplace, they can be appropriately and adequately held to account by their managers.
This is not the case for MP's, some of whom are allowed to treat being a Member of Parliament as a part time job, and only face a review of their performance as a representative of their constituents every five years at General Elections.