Boris Johnson has used his column in the Daily Telegraph to appeal to party colleagues to accept the "bossyboots brigade" he so often rails against are right in the case of a smoking ban in cars where children are present.
"Surely to goodness - you might say - people these days are aware of the problem of passive smoking? Surely all smokers know that they shouldn't be puffing away in a car, while the pink defenceless lungs of kids are sucking in the evil vapours?" he wrote.
"Alas, I am afraid that people either don't know, or don't care enough.""These kids cannot protest, and very often the smoker in the vehicle lacks the will to stub it out. "This law would give that smoker that extra legal imperative to obey their conscience and do the right thing."
Rejecting critics' claims that it would divert police resources from more serious crimes, he said it would be "largely enforced by the natural social pressure of disapproval backed by law".
More top news
The party's deputy-leader is the sole candidate in the race to succeed Gerry Adams.