Once your solicitor has exchanged legal contracts on your sale/ purchase and set a completion date for your move you should inform the following :

British Gas
Southern Electric
Thames Water
BT/Comtel
Post Office Redirection Service
Cancel Newspapers/Milk
Organise a Removal Company
Bank
Dentist
Doctor
Employer
New and Old Council
Friends and Relatives
Defrost Your Freezer
Ensure Your Pets Are Taken Care Of
Tax Office/Accountant
Cancel or Rearrange Relevant Direct Debits/Standing Orders
Driving Licence
Your Pension and Insurance Companies
Credit/Loan Companies

This list is not exhaustive