Motor vehicles on UK roads must have a valid MoT certificate (VT20).
The motor vehicle test is an annual test of the features of motor vehicles which are known to cause accidents, and thus focuses on relevant safety features including lights, brakes, steering etc.
The MoT test is due on or before the expiry date, which is shown on the VT20.
Your car must have a MoT every year, which can be up to a month early (providing the old test certificate is produced).
The issue date of the new certificate will be the day the new test was taken, however the expiry date will be the same as the old VT20 plus one year.