Question about MOT test (UK).?

Not if it's a roadworthiness issue. Basically things like steering, suspension, tyres, and so on. Clearly that would not include things like an empty washer bottle, failed wipers, blown headlamp bulbs. Although those can be roadworthiness issues if it's raining or is dark.

The MOT test is irrelevant in those respects in that whenever the car has a roadworthiness failure it becomes illegal to drive on public roads or on private land to which the public have unobstructed access. The difference these days is that now MOTs are recorded via an online database so if you do insist on driving away an unroadworthy car after a test failure that failure and the reason will have been recorded and the police can get the results instantly if they stop you. With the old paper based system you could get away with claiming that the fault had only just occurred and you'd been unaware of it; police simply had no realistic way of consulting all MOT centres to find whether one had failed your vehicle recently but could only tell whether an MOT examination was overdue.

If it fails the MOT and you know there is something wrong with it, you are not legally allowed to drive it on the road, even tho the previous MOT has not yet run out

Official: https://www.gov.uk/getting-an-mot/after-the-test

Driving a vehicle that’s failed

You can take your vehicle away if your MOT certificate is still valid.

... your vehicle still needs to meet the minimum standards of roadworthiness at all times or you can be fined

Yes you can take it away if the test centre allows you to. But if it's a major road safety failure you can be charged with having an un-roadworthy car any time you are stopped.

Should you choose to drive a dangerous car away from a test centre the examiner my consider it his/her duty to report the fact to the police.

No. Once it fails the failure forbids you from driving.