Hello Nigel. It is certainly possible to freeze a large block of cheddar cheese for later use on pizza.
To achieve the best results, you should grate the cheese while it is still very cold. Once shredded, I recommend tossing it with a small amount of cornstarch or flour to prevent the pieces from sticking together into a solid mass. You should then store the cheese in an airtight freezer bag with the excess air squeezed out.
Please keep in mind that the freezing process will change the texture of the cheese, making it more crumbly. While this makes it less suitable for eating fresh, it will still melt beautifully on your pizza.