Bhg481 is, indeed, correct. You can have your car MOT'd every day if you're mad enough to do so (or, indeed, several times every day if you're even madder than that). However you only get a '12 month' MOT certificate if you put your car in for the test with more than a month left on its existing certificate (rathe than the '12-and-a-bit' months you can get when there's less than a month left on it).
>>> "I understand if it fails, I can’t rely on the old previous MOT valid to date".
It's important to understand that there are two entirely separate offences that are relevant here:
(i) using a vehicle on a public road without a valid MOT cerficate ; and
(ii) using an unroadworthy vehicle.
If you put a vehicle in for its MOT test early, and it fails the test, the old MOT certificate remains VALID and you CAN'T be convicted for not having a valid certificate (even if it's got four bald tyres, smoke pouring out of the exhaust and bits hanging off it).
If the test failure was due to the vehicle being unroadworthy (and you continue to drive the vehicle) you CAN be successfully prosecuted for driving an unroadworthy vehicle but that would have applied anyway, even if you'd not put the vehicle in for a test.
If the test failure is for something not related to the roadworthiness of the vehicle (e.g. because the steering lock doesn't engage when you remove the keys from the ignition) then you can continue to drive the vehicle (using its old MOT certificate) without fear of prosecution.