Some years ago, when the RAF had actually stopped ME training (the Pigs were dead and the Wetdreams were grounded after CFS had a double hush), it certainly was 'FJ or bust'. You had to have got as far as a FJ OCU to stand a chance of getting restreamed to ME if you were binned from your OCU.
I was at Brawdy at the time as a student on 234. One day, fairly early in the course, one of the staff came in and said "Of course, if anyone's finding it hard going, you can always volunteer for helicopters..." He said it as a joke, but 2 people took him at his word, went to see the Boss and asked for a transfer. Their bags were packed and they were off the stn in less than a week. Not to rotary training though, but to the Aircrew Reselection Board at Biggin Hill. We never heard what became of them after that......