What are the functions and processes of Parliament in holding the Executive to account?

The role of Parliament is split between the House of Commons and the House of Lords, and they both have different but compatible roles in holding the government to account over policy, actions and legislation proposed by the Executive (Government). The House of Commons, has an official opposition which is normally the second largest political party in the Commons as the largest party makes up the Government. They are afforded time to hold the Executive to account through Prime Minister's Questions, Questions to Ministers and Urgent Questions. These sessions enable direct scrutiny of members of the executive in their ongoing actions, as well as during the legislative policy process. Furthermore, the House of Commons forms many Departmental Select Committees, with one for each Government department such as foreign policy or agriculture. The committees are representative of the number of MPs per party within the Commons, and the Chairs are decided between parties. These are extremely effective with notable cases such as former Conservative MP Dr Sarah Wollaston criticizing, Chair of Health and Social Care Committee, releasing a scathing report of her own party in Government, and Yvette Cooper as Chair of the Home Affairs Committe effectively making the then Home Secretary Amber Rudd resign over the Windrush Scandal. This shows their are functions and abilities of the Commons that can hold the Executive to account.The House of Lords has similar abilities in their own departmental Committees but the main powers of the House of Lords lie within their political impartiality and the fact that there is a non-government majority in the House of Lords. Due to the impartiality of the members in the HoL, they are not forced to vote along party lines and can rebel or oppose with no consequences unlike MPs. The reason for the impartiality of Peers in the HoL is down to many of them being experts in their fields, having reached the top of their careers. Such as Professor Robert Winston who can advise on scientific and ethical matters due to his career and his seniority in his field. This creates the atmosphere of greater scrutiny upon the government, and combined with a non-government majority means that the Executive regularly have to revise and rethink policy so that it is not defeated.