If you're switching to or from a cable network, you will need to contact your new provider to place an order for your new service or services.
If you choose to keep your existing 'phone number, your new provider should notify the provider you are leaving that the service is being transferred (although you may not be able to keep your existing landline number if you are switching landline provider at the same time as moving home).
If you are switching your landline only and you have asked to keep your existing phone number, you would not normally need to notify the provider you are leaving that you are moving to a new provider (though you may want to check whether the provider you are leaving will charge an early termination fee for leaving your contract).
You'll most likely use this process if you're switching services with providers that are delivered over different networks.
For example, if you're switching to or from the Virgin Media cable network.
If, however, you choose to obtain a new landline telephone number from your new provider, then you will need to contact both your current provider to cancel your contract and your new provider to arrange your new landline telephone service.
You may decide to coordinate the start of your new service with the end of your old service, or you may wish to have an overlap of your old and new contracts.
If you're following a cease and re-provide process, you will normally receive notification from the provider you are leaving that your contract is ending (and notification of any charges associated with this), and you will be given a new contract from your new provider which will tell you when your contract is due to start.
Note that if you use this process and a new line needs to be installed to your house, you may be liable for the cost of this installation.