Britain is in the slow lane. The report from the OECD today shows that the UK economy next year is forecast to grow at just one per cent — less than half the speed of the US, Canada or Germany.

In the space of a year, we’ve gone from one of the strongest of the major advanced economies in the world to the weakest. The European economies we were told by the Brexiteers were basket-cases — like Italy and France — are now set to outpace us. What is the reason?

Partly it’s because the fall in the pound has hit real incomes. Anyone who went overseas on holiday this summer will know that you don’t get as many euros and dollars for your pounds at the bureau de change.

The same effect is causing the cost of imports to rise. That increases inflation — as today’s latest numbers on shop prices show — and that, in turn, reduces real incomes.

It’s sad that those who voted for Brexit because they apparently felt “left behind” by the growing economy are the very people who are now seeing their living standards fall.

On the other hand, the devaluation has, in the OECD’s words, only “modestly” improved Britain’s export performance. Once again, Britain has learned the lesson that you can’t take the easy route of devaluing your way into becoming an export champion — you have to do the hard work of improving your productivity, an area where Britain still lags behind its neighbours and which breaking away from our main export markets will hardly help.

Shambolic

Another cause of Britain’s further slowdown is what the OECD describes as “uncertainty” over the future direction of the Brexit negotiations. That’s putting it mildly.

This week the whole world has been treated to the shambolic spectacle of the Cabinet negotiating with itself in public.

Britain’s diplomatic mission to the United Nations in New York looks like something that Alan Ayckbourn could have written: the dishevelled Foreign Secretary who gives a press conference trapped in a hotel lift; the Prime Minister who’d rather have a meeting with Ivanka Trump than with Boris Johnson.

The truth is that more than a year after the referendum and the creation of the May government, there is still no agreement on what we are asking the Europeans for — and the arrogant assumption is that once we finally decide among ourselves, the Europeans will give it us.

Once again in the Brexit talks it is worth listening to the actual words of the EU. It makes it very clear that if Britain wants a transition agreement after we leave in 2019 — and it is universally agreed across Whitehall that we do — then we will have to accept an existing, off-the-shelf arrangement.

If we want to remain trading in the single market and customs union, then we will have to make annual financial contributions, accept free movement of people and acknowledge the jurisdiction of the European Court of Justice.

That is what Mrs May was sensibly shaping up to offer in Florence, until Mr Johnson suddenly realised it would run counter to all the promises he made a year ago.

The reputed offer of €20 billion is the opening move, though Downing Street privately could concede double that in the end game.

As our exclusive interview with Ireland’s EU Commissioner shows, the EU is hoping that Mr Johnson’s very public tantrum has not affected Mrs May’s cool calculation that ending the damaging uncertainty about life immediately after Brexit is in Britain’s vital economic interest.

We shall see. The fact that the Prime Minister has to give her speech in Florence flanked by her Foreign Secretary, Chancellor and Brexit Secretary may be intended as a show of unity but is, of course, an admission of weakness.

All the while, today’s economic numbers remind us the British people are paying a high ticket price for this particular political farce.