Copyright falls under intellectual property rights. For information on that please see here. Copyright is very important to any creator but especially to voiceover artists. As a voiceover artist it is not legally possible to sign away your copyright. So you will always own the copyright to the material you recorded. Therefore your voiceover audio is only ever licenced for use on agreed platforms. You can find further information here. Intellectual Property Office
The laws have a framework so that people can see how work can be used. Responsibilities of people, as well as the rights of the owner are set out. What can you do with your work? Well you could copy, change, sell it, share it online, rent it or prevent other people from doing those things to it. When someone hears your voice played out whether it be online or downloaded to a device then they are interacting with copyright. The piece of work should be either original or tangible.
So for a work to be original you must have produced it yourself i.e. spoken it. Tangible means that the idea would have to be expressed in some sort of physical form so when you speak a phrase then it is only protected the moment you record it. Once recorded, it is protected.
But how do I protect my work?
As soon as your work is created or in voiceover world as soon as you have recorded it in audio form. There is no need to register this work unlike a patent or a trademark.
How long will your work be protected for?
A short answer is that it depends on factors such as the type of work created and when it was made. Generally the shortest length of time for protection is 50 years. But it could be 70 or more.
With the potential European relationship process underway, updates to legislation and copyrighted works will continue to be protected as there are other international treaties covering this. Examples of these treaties include the The Berne Convention and the TRIPS agreements.
Note that copyright may not cover all forms of creative work so Intellectual property may be more suitable. But do remember that it is illegal under UK law for a voiceover artist to sign away their copyright.