What are the functions of parliament?

Parliament can scrutinise government legislative proposals.
Parliament can scrutinise the actions of the executive and ensure they are accountable to their actions – the convention of individual ministerial responsibility states that ministers are accountable to parliament.
Ministers who mislead parliament may be required to resign.
Scrutiny of the exec.

Parliament helps maintain the legitimacy through scrutiny, accountability and through debates but, legitimacy in the House of Lords is limited because it is unelected.
In terms of the House of Commons, public trust in parliament has declined after the ‘cash for questions’ scandal in the 1990’s; some MP’s accepted money to table parliamentary questions, and especially when revelations were made by the Daily Telegraph in May 2009 about the MP expenses scandal. 4 Labour MP’s faced criminal charges.