The conventional wisdom is that the 2010 intake, who make up almost half the Parliamentary Conservative Party, are more libertarian than those who came before – social liberals and fiscal hawks, who represent a Thatcher’s Children generation.

Their record on some issues backs that up – their near-universal support for austerity and strong opposition to ID cards, for example, but it isn’t a fully accurate stereotype.

Libertarianism is often unfairly characterised as an unwordly idealism. In this instance, opponents of the idea drew a pragmatic case against more regulation. Defenders of personal and family responsibility united with those who were concerned the law would be an unenforceable waste of police time – including Theresa May, not renowned as an unworldly idealist.

For an insight into the case those opponents made, it’s worth reading the blogposts on the topic by Robert Halfon and Steve Baker. Neither lives down to the “who cares” caricature painted by critics of the libertarian position. Both argue instead that a ban is a bad way to pursue a desirable goal.

Most of their fellow Conservatives disagreed with them and voted for it, by a margin of 55 per cent to 45 per cent. But did MPs divide along generational lines, as conventional wisdom suggests they would?

Well, not exactly.

Here’s the split from each generation of MPs, classified by when they were first elected:

Smoking Split

(NB It’s important to note that this is expressed as a percentage in order to give an idea of the split in each cohort. The older groups of MPs are smaller – in total, 23 Conservative MPs of the pre-1992 vintage voted, while 116 of the 2010 intake took part, hence the graph changing from volatile differences to more nuanced divides as you read from left to right. I also haven’t included those who abstained (1 MP) or didn’t vote (76 MPs).)

While MPs first elected in 2005-2010 were quite evenly split (53 per cent for to 47 per cent against), the latest intake divided 62 per cent to 38 per cent in favour of the measure.

The issue at hand wasn’t a perfect litmus test of libertarianism, indeed some freedom-loving MPs like Dom Raab voted for it, but the result is still challenging to widely held assumptions about the ideology of newer MPs.

It is also interesting that such a large majority of the 2010 intake supported the proposal despite the opposition of the Home Secretary, the Justice Secretary and the Policing Minister. In a free vote, with cabinet ministers backing each side, the outcome can’t really be attributed to patronage or payroll.