Peter Day is (mostly!) talking a load of BS. Although he is right in so far as Radio budgets are tighter than those in TV and so I am sure it is much harder for a Radio journalist to wangle J travel.
BBC allows J on flights of more than four hours for executives, and that includes certain journalists who have a certain seniority or those whose contracts and relationships with the corporation are negotiated by talent agents.
I have worked with John Simpson and Jeremy Paxman and both flew J with my team to CAI and LEN.
I myself flew J to SVO, IAD, EWR and LAS when I was a BBC employee many moons ago, and I was far from senior! I just happened to find cheaper J tickets myself than the economy fares proposed by Carlson Wagonlit who were then the in house BBC travel agents. I managed to get accounts to refund my amex just fine.
I have also seen plenty of talent in F when on BBC business... the Top Gear trio always flies F for example.
Sir David Attenborough is a unique exception, prefering to fly in Y with the crew, even in recent years when age has caught up with him.