Most vehicles that are older than three years must by law go through yearly roadworthiness checks. The MOT test makes sure that a vehicle meets the government's road safety and environmental standards.
The MOT certificate
The MOT certificate confirms that at the time of the test, without dismantling it, the vehicle met the minimum acceptable environmental and road safety standards required by law. It doesn't mean that the vehicle is roadworthy for the length of time the certificate is valid. The MOT certificate is also no guarantee of the general mechanical condition of your vehicle. The test doesn't cover the condition of the engine, clutch or gearbox.
You can have your vehicle tested up to one calendar month in advance and keep the anniversary of the of the current expiry date.