Real GDP per capita growth for US vs UK was almost identical until 2008. The last 3 years have been terrible for the UK, but if you're looking for the start of UK's stagnation you have to go much farther back than Brexit.
The problem I see is that although the trend may have started before, Brexit caused the local financial services sector to effectively collapse and move to the Netherlands and Germany. London will never be able to recover that loss in ten generations. Had brexiters not ejected your finance industry, there was probably an opportunity to recover.
As far as I am aware, this is just straight up is not true. Do you have a source for this? Because if the financial sector in the UK halved and moved into the Netherlands and Germany the UK would be doing much, much worse, and Germany much better economically.
This - the economy rode on financialisation and north sea oil for the two decades before 2008. Since 2008 there has been no real action to resolve the core issue of unlocking the potential of the North of England - everyone knows that that is low hanging fruit (human capital, regional infrastructure etc) but no one will actually take the risk and go for it.
