Failed test - progress minus in the jargon
The examiner in effect considers whether he would find it frustrating following somebody so slow. Obviously though, there is a problem if a sign is missing - perhaps another argument for having a camera on board so you can appeal the verdict. BTW, on the examiner's own test to get the job, you need to drive as fast as is safely and legally possible. So, on the motorway 65= Fail, 75= Fail, unless the tester agrees the conditions require it.