Chris Mason: Rishi Sunak's smoking move gets cross-party backing

For all the arguments about HS2, perhaps Rishi Sunak's announcement on smoking could be the most profound and long-lasting.

Labour are not seeking to oppose it. The Welsh and Scottish governments are making positive noises too.

A Conservative prime minister makes a party conference announcement, and within hours SNP and Labour ministers in Edinburgh and Cardiff respectively sound like they broadly agree.

To put it gently, that doesn't happen very often.

And this matters, because the laws on smoking are devolved. The government at Westminster decides policy for England only.

Let's be clear: those at Holyrood and in the Senedd are not copying, latching on to an idea that had never crossed their minds before.

Political instincts on this issue are coalescing around a similar position.

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The prime minister told the Today programme on Radio 4 that his plans to phase out the sale of cigarettes in England will be the "biggest public health intervention in a generation".

England's Chief Medical Officer, Sir Chris Whitty - remember him from all those pandemic announcements - chimed in on how beneficial the health improvements would be.

So is this a moment rather like the ban on smoking in public places? Or gay marriage?

Political ideas that provoked a debate, but quickly became baked in - with next to no prospect of ever being reversed.

Hang on a minute: there is a complicating twist here.

When governments in recent years have passed a law to ban things or allow things, that ban or right has been universal.

Or, at least, universal for adults - and where there was a universal understanding of what an adult is.

The moving target of a steadily rising age at which cigarettes can be bought legally is more complicated.

If it happens, the oddities of it may seem minimal in the early years.

But over time, they would become more, well, odd.

Fraser Nelson, the editor of The Spectator magazine, extended the logic of the plan neatly here.

Would it involve shopkeepers having to ask middle-aged folk and older, over time, for ID, to work out which side of the ever moving line of legality they are on?

Ministers will hope the effect of the law will more than compensate for its absurdities.

That an already falling propensity to smoke across society - and among younger generations - will be accelerated to the point that the legal niceties become irrelevant.

It is not long ago that it felt like cigarette smoke was almost everywhere: in pubs and clubs, even on public transport and at work.

That now seems like another world.

But will this idea - complete as it is with quirks - manage to achieve its aim of eventually eradicating smoking almost entirely?

There is the political will for that to happen. But bringing it about is tricky.