Examiners have an easier job when people pass as they can put their feet up for 5 minutes instead of having to write a detailed report. And they don't 'fail you', test candidates do that themselves, the examiner just observes and records what you do. You will have been told why you have not passed, so if you still don't know what is wrong then you are clearly not listening to their advice.
Examiners are paid a wage and they earn that wage irrespective of people such as you passing or failing the driving test.
It seems to me that you are simply not receiving the quality of training that you need in order to reach the basic standard of safety required, and that being the case you will continue to fail at Sheffield Middlewood or any other test centre.
You need to stop blaming the examiners and start looking at your own preparation.
Regards
Don L Gates @UK Driving Skills