Hi,
Sorry to hear about your unfortunate experience whilst on your course. SEP for most people is stressful but ultimately necessary to get the job! The CAA set down rules which airlines have to follow and this includes Cabin Crew Training and the associated Pass Marks. In your case you failed your 1st exam and then the re-sit. This results in what VS call a "Viva" and I think you really should have carried on. People learn and absorb new information in different ways, some are quick, others not. Some people prefer to read and others prefer more demonstrative learning. It could just have been that the written exams were bogging you down a bit and your Viva would have been a different and in most cases succesful exam bringing you back on track. I coudn't comment on your individual case as your circumstances are unique but I don't think VS would hold your past experience against you, employment laws are just too strict!
There are all sorts of stupid rumours surrounding the airline industry and Virgin (only blondes need apply, young crew only etc) and all are nonsense. I think you should put your thoughts into a well written letter, indicating your desire to re-join and see what happens. Next time though, don't give up if you find it tough, keep going and you'll get through. But maybe this just isn't the right path for you at the moment. Either way, good luck and maybe we'll see you flying the friendly skies at VS.