It is usually politicians who are brought down by preaching one thing and then being found to be practising quite the opposite. But now it is another of our moral guardians which has been found wanting - Greenpeace have admitted one of their directors, Pascal Husting, regularly commutes by air from his home in Luxembourg to the NGO's HQ in Amsterdam.
Husting's defence - that he has a young family, the train journey is a 12 hour round trip, and that the arrangement was only meant to be temporary - would stand up for anybody other than a senior staffer of an organisation which has campaigned fiercely against air travel.
While I respect Greenpeace and their aims, I've always been uncomfortable with that NGO tendency to preach at those who 'don't get it'. And, if you are going to make environmental protection a moral issue, then you cannot, and must not, live a high-carbon lifestyle out of convenience - because that's exactly what you are criticising others for doing.
It all comes down to authenticity - being what you say you are. If you are going to lead on sustainability, whether in an organisation or in public life, then you must be seen to walk the walk as well as talk the talk. Set the standard for everyone and stick to it yourself, because people believe what they see, not what they read.
The coda is that a chastened Husting is now taking the train.