There is a new service on the government website which allows you to print your own MOT certificates if you have lost or damaged one.
Click here to see it.
This is the same website where you can check any car for MOT related issues and gives you an idea of a cars history.
They have added a button that allows you to view the test certificate - from there you enter the document number from your car registration document (V5) and you can print your own certificate.