Just some reality
About 6.5% of German cars come to the UK.
About 2.6% of German GDP is exported to UK including the 6.5% cars
France exports about 1.4% of GDP to the UK.
The internal EU market is of great importance to EU member states including Germany and France although the UK is an important market a unified Europe is a first priority.
Within the exports to the UK you also have to look at the Rotterdam effect these are European goods passing through the UK to markets beyond. They are calculated into the UK import figures and no one has done the maths on the real effect.
US 19.39 Trillion very difficult for major economies to cut trade deals with and the UK will always be a fringe player here while a major player in the EU.
EU 18.7 Trillion UK already has trade deals.
UK 2.66 Trillion
On a per capita basis the UK is the 28th wealthiest country in the world.
You can say exports to the EU are falling however you can’t calculate the build-on factor growing what you already have. The strategy that most business utilise in order to survive.
Even the Iceni traded with their closest neighbour Europe especially the Italians!
This does not cover all the other disruption airlines, travel ,travel insurance, medical issues, citizens rights, plus the 1000s of non-tariffs that have to be negotiated. Also not to mention the Irish border and Gibraltar. It takes many years to negotiate trade deals there are many precedents for such trade arrangements. Also the current political class don’t seem to have the abilities required to manage a go it alone position.