When the government plan to put the building of a third runway at Heathrow to parliament was revealed after someone photographed it on the tube, John McDonnell appeared on Channel 4 News.
Though the shadow chancellor is a longstanding opponent of the idea, in that interview he spent most of his time rubbishing the idea that collective cabinet responsibility could be suspended for the Commons vote.
Similarly, Tim Farron's statement on the subject began:
The suggestion that there might be a free vote on Heathrow is farcical – this is a huge decision and the Conservative government has to make a collective decision and take full responsibility. If people disagree they can resign.But is the public greatly interested in the details of how the vote will be handled at Westminster?
I can imagine people being against a third runway because their lives will be affected by aircraft noise or because they think it will be bad for the environment more generally.
I can imagine them being in favour of it because they think it will be good for the economy.
I find it much harder to imagine people being much concerned by whether there is a free vote or not.
In fact to most voters the idea that politicians will vote in accord with what they believe rather than they way their party tells them will be rather attractive.
I am willing to believe a free vote in impractical, and opposing it might chime with the narrative that this is an incompetent government. But I can't see this line of attack moving many voters.
We Liberal Democrats would do better to emphasise the second paragraph of Tim's statement (which should have been the first):
Liberal Democrats are the only party consistently opposed to a third runway at Heathrow and we will fight any plans to allow it to be built.That will interest many voters.