So why did General Motors really decide to bail out of the European market after persevering for so long? As boss Mary Barra pointed out, GM took over control of Opel in 1929 and Vauxhall in 1925.

What’s more, GM had the perfect opportunity to throw in the towel on Opel/Vauxhall in 2009, when it filed for bankruptcy and came within a whisker of selling off its European arm to component giant Magna.

At this morning’s press conference, Mary Barra twice said the decision to sell was because of "key fundamental shifts" in European markets over the past 12 months. She listed them as "changes in customer preference to geopolitical and regulatory environments to the impact of technology".

Clearly, geopolitics meant Brexit, which GM has already blamed for missing its aim of breaking even in Europe after over a decade of losses. The fall in the value of the pound against the euro put a dent in GM’s accounts.

Read the latest on PSA's purchase of Opel/Vauxhall

As for "changes in the regulatory environment", I would suggest that this is probably a reference to the impact of the Volkswagen emissions scandal.

GM Europe sold just over 1.1 million cars last year, and it has to meet the EU2020 C02 fleet average laws. The coming introduction of the RDE real-world solution tests will probably mean nearly all of its diesel cars would need to be fitted with urea injection. That would be expensive to implement and might not even be possible on some older models.

Deleting diesel engines altogether from some models would have been another hurdle, and it seems likely that all petrol engines will soon have to be adapted to use a particulate filter. A shift to petrol engines for most of its models in the Astra and Corsa ranges would probably have meant investment in mild hybrid technology, such as electric turbocharging systems.

This sudden shift towards petrol engines and, eventually, hybridisation for smaller cars and the need to install more expensive diesel engines in larger cars was probably an investment too far for the GM board, especially with such a relatively small European business.

Indeed, Opel/Vauxhall was specifically singled out with three other makers last December in a report by the European Environment Agency, which said Opel would have to "quicken its pace in CO2 reduction" if it was to hit the 2020 targets.

But there was another fascinating insight into GM Europe’s predicament at this morning’s press conference with the PSA Group. GM president Dan Ammann slipped out the fact that, in the next few years, just 20% of Opel/Vauxhall vehicles would have been common with GM’s global range.

As auto analysts at Evercore pointed out a couple of weeks ago, European market cars - even superminis and medium hatches such as the Astra - are expensive to engineer and surprisingly sophisticated compared with similar-size vehicles sold in other global markets.

In other words, GM could not sell most of its unique European models in other markets, further undermining the financial case for keeping the Opel and Vauxhall brands. On top of that, GM Europe’s two new SUV models - the Grandland X and Crossland X - were built on PSA Group platforms.

The final big insight came at the end of the conference, when PSA boss Carlos Tavares was being quizzed on the likelihood of redundancies and plant closures. Discussing Brexit, he said that a ‘soft’ Brexit might not make too much difference, but a ‘hard' Brexit would mean that UK government hints at helping to build up the country’s diminished component supply network would become crucial.

Tavares said a hard Brexit raised the prospect of a "UK supply" of PSA Group cars being sourced in the UK. But that would mean considerably more of any new PSA-based vehicle would have to be made in the UK. As Tavares put it, the supply base needs to be in pounds in order for it to be matched to revenue that is in pounds.

Ellesmere Port is safe for another four years. But in that time, the UK has to do a huge amount in order to rebuild its auto component supply chain before the Vauxhall plant will be refitted with PSA Group production lines. Once the UK leaves the EU, the days of freely shipping components backwards and forwards across the continent could come to an end.

Vauxhall and Ellesmere Port can live again under French control, but it will take a huge effort from government and other UK-based makers to make more of every car in the UK.

Read Autocar's Vauxhall Astra review