If you have been on copper or just Fibre to the cabinet with the previous provider, there's no reason that the service should have to stop. It could carry on until you are sure that the new installation and service is fully up and running with Talktalk, @bigal60.
I would keep it to fall back on myself!
They use different infrastructure. If you are already on Full Fibre with another company, there's more likely to be a hiatus.
