If your vehicle has failed its MOT when the certificate is still live:
You may take your vehicle for its MOT test up to a month before your current certificate ends; the exact date will be on your MOT certificate. This had led to people questioning whether they can drive it after it has failed as they still have a valid certificate.
The answer is that you can still drive your vehicle if it fails the test and its existing MOT certificate is still valid (i.e. if your test was before the expiry date) as long as no ‘dangerous’ problem(s) were listed in the MOT.
If you drive with ‘dangerous’ problem(s) listed in your MOT you can be fined up to £2,500, be banned from driving and get 3 penalty points.
However the fact that your vehicle has failed its MOT means there are faults with the vehicle, even if they haven’t been classed as ‘dangerous’ and if you do get stopped by the police you could be prosecuted if your vehicle is not roadworthy.
Though you still have a valid certificate you could be breaking the law by using a vehicle with a known fault on the road, it is highly recommended to get the repairs fixed as soon as possible and not to drive the vehicle in the meantime.