UK Government & UK Parliament
How to find your MP (Member of Parliament): parliament.uk
How to find your MEP (Member of the European Parliament): europarl.org.uk
Contact your Councillors, MP, MEPs, MSPs, or Northern Ireland, Welsh and London AMs for free: writetothem.com
Find out what your MP is doing in your name, read debates and sign up for email alerts: theyworkforyou.com
How to find a Lord: writetothem.com/lords (Lords are not elected and do not have a duty to reply to the public but they may be able to help or influence national legislation and other Parliamentary matters. Lords do not have constituencies like MPs, so you may contact any of them).
The Parliamentary and Health Service Ombudsman looks into complaints where an individual believes there has been injustice or hardship because an organisation has not acted properly or fairly or has given a poor service and not put things right.